Chapter 17 Electrodiagnostics

Question 1

Electrodiagnostic studies (also known as NCS/EMG or sometimes just EMG) include nerve conduction studies (NCSs or NCVs) and EMG. Other less commonly performed electrodiagnostic tests include somatosensory evoked potentials, brainstem auditory evoked potentials or responses, _________-_________ EMG (SFEMG), repetitive stimulation studies, and _________ skin response. This test provides _________ information about nerves and muscles in real time. It gives information about muscle and nerve _________, unlike most radiologic studies, which give a static picture of anatomy and do not directly assess function.

Answer 1

Electrodiagnostic studies (also known as NCS/EMG or sometimes just EMG) include nerve conduction studies (NCSs or NCVs) and EMG. Other less commonly performed electrodiagnostic tests include somatosensory evoked potentials, brainstem auditory evoked potentials or responses, single-fiber EMG (SFEMG), repetitive stimulation studies, and sympathetic skin response. This test provides physiologic information about nerves and muscles in real time. It gives information about muscle and nerve function, unlike most radiologic studies, which give a static picture of anatomy and do not directly assess function.

Question 2

Electrodiagnostic studies:
Indications for electrodiagnostic testing include _________, tingling/_________, pain, weakness, atrophy, depressed deep tendon reflexes, and/or fatigue.

Answer 2

Electrodiagnostic studies:
Indications for electrodiagnostic testing include numbness, tingling/paresthesias, pain, weakness, atrophy, depressed deep tendon reflexes, and/or fatigue.

Question 3

Electrodiagnostic studies:
EMG/NCS can serve as an important part of a patient’s clinical picture. Electrodiagnostic tests are used to (1) establish a correct _________, (2) localize a _________, (3) determine the _________ when a diagnosis is already known, and (4) provide information about the prognosis. NCS/EMG should be considered an extension of a good history and physical examination.

Answer 3

Electrodiagnostic studies:
EMG/NCS can serve as an important part of a patient’s clinical picture. Electrodiagnostic tests are used to (1) establish a correct diagnosis, (2) localize a lesion, (3) determine the treatment when a diagnosis is already known, and (4) provide information about the prognosis. NCS/EMG should be considered an extension of a good history and physical examination.

Question 4

INITIAL SETTINGS FOR NCS
1. _________ speed is the horizontal axis on the recording in units of time (milliseconds [ms]). _________ is the vertical axis on the graph in units of voltage (millivolts [mV] for motor studies or microvolts [μV] for sensory studies).
2. Motor settings: sweep – 2 ms/division, gain – 5 mV/division.
3. Sensory settings: sweep – 2 ms/division, gain – 20 μV/division.

Answer 4

INITIAL SETTINGS FOR NCS
1. Sweep speed is the horizontal axis on the recording in units of time (milliseconds [ms]). Gain is the vertical axis on the graph in units of voltage (millivolts [mV] for motor studies or microvolts [μV] for sensory studies).
2. Motor settings: sweep – 2 ms/division, gain – 5 mV/division.
3. Sensory settings: sweep – 2 ms/division, gain – 20 μV/division.

Question 5

INITIAL SETTINGS FOR EMG
1. Sweep speed: _________ ms/division
2. Low-frequency filter: _________ to _________ Hz
3. High-frequency filter: _________ to _________ Hz
4. Amplifier sensitivity: _________ to _________ μV

Answer 5

INITIAL SETTINGS FOR EMG
1. Sweep speed: 10 ms/division
2. Low-frequency filter: 10 to 30 Hz
3. High-frequency filter: 10,000 to 20,000 Hz
4. Amplifier sensitivity: 50 to 100 μV

Question 6

INTRODUCTION TO NCS
NCS is the recording of an electrical response of a _________ (via an electrode over that _________ or a _________) that is stimulated (electrically depolarized using a probe) at one or more sites along its course. The action potential (AP) that is propagated is the summative response of many individual axons or muscle fibers.

Answer 6

INTRODUCTION TO NCS
NCS is the recording of an electrical response of a nerve (via an electrode over that nerve or a muscle) that is stimulated (electrically depolarized using a probe) at one or more sites along its course. The action potential (AP) that is propagated is the summative response of many individual axons or muscle fibers.

Question 7

INTRODUCTION TO NCS
For motor nerves, this response is called a _________ motor action potential (CMAP) and represents the _________ response of motor units (MUs) that are firing. CMAPs are usually recorded in _________.

Answer 7

INTRODUCTION TO NCS
For motor nerves, this response is called a compound motor action potential (CMAP) and represents the summative response of motor units (MUs) that are firing. CMAPs are usually recorded in mV.

Question 8

INTRODUCTION TO NCS
For sensory nerves, the response is called an SNAP and represents the _________ of individual sensory nerve fibers. SNAPs are very small-amplitude potentials that are usually recorded in _________. Late responses (evoked potentials that record over a very long pathway) include _________ waves and _________-reflexes.

Answer 8

INTRODUCTION TO NCS
For sensory nerves, the response is called an SNAP and represents the summation of individual sensory nerve fibers. SNAPs are very small-amplitude potentials that are usually recorded in μV. Late responses (evoked potentials that record over a very long pathway) include F waves and H-reflexes.

Question 9

INTRODUCTION TO NCS
Orthodromic refers to conduction in the _________ direction as occurs physiologically (i.e., a sensory fiber conducts from the extremity toward the spine). Antidromic refers to conduction in the _________ direction to the physiological direction.

Answer 9

INTRODUCTION TO NCS
Orthodromic refers to conduction in the same direction as occurs physiologically (i.e., a sensory fiber conducts from the extremity toward the spine). Antidromic refers to conduction in the opposite direction to the physiological direction.

Question 10

Components of the AP
Latency is the time it takes from stimulation to the beginning of the AP (the speed of transmission). The latency of a sensory nerve is dependent on the conduction speed of the _________ fibers and the distance it travels. The latency of a motor nerve also includes the time it takes for the AP to synapse at the _________ and the speed of conduction of the electrical potential through the muscle. Since there is no _________ _________ of sensory nerves, the latency of a sensory nerve is directly related to the conduction velocity (CV).

Answer 10

Components of the AP
Latency is the time it takes from stimulation to the beginning of the AP (the speed of transmission). The latency of a sensory nerve is dependent on the conduction speed of the fastest fibers and the distance it travels. The latency of a motor nerve also includes the time it takes for the AP to synapse at the NMJ and the speed of conduction of the electrical potential through the muscle. Since there is no myoneural junction of sensory nerves, the latency of a sensory nerve is directly related to the conduction velocity (CV).

Question 11

Components of the AP
Latency measurement requires standardized and accurately recorded _________ or else the results are meaningless.

Answer 11

Components of the AP
Latency measurement requires standardized and accurately recorded distance or else the results are meaningless.

Question 12

Components of the AP
Conduction velocity reflects how fast the nerve AP is propagating. In sensory studies, the velocity is measured directly from the time it takes the AP to travel the measured distance (distance/latency). In a motor nerve, two different sites have to be stimulated to calculate the velocity (velocity = change in distance/change in time) and account for the myoneural junction. The presence of a myelin covering speeds up NCV via a process known as _________ conduction. Myelinated nerves conduct impulses approximately _________ times faster than unmyelinated nerves. In myelinated nerves, the CV is primarily dependent on the integrity of the _________ covering. Slowing or latency prolongation usually implies demyelination.

Answer 12

Components of the AP
Conduction velocity reflects how fast the nerve AP is propagating. In sensory studies, the velocity is measured directly from the time it takes the AP to travel the measured distance (distance/latency). In a motor nerve, two different sites have to be stimulated to calculate the velocity (velocity = change in distance/change in time) and account for the myoneural junction. The presence of a myelin covering speeds up NCV via a process known as saltatory conduction. Myelinated nerves conduct impulses approximately 50 times faster than unmyelinated nerves. In myelinated nerves, the CV is primarily dependent on the integrity of the myelin covering. Slowing or latency prolongation usually implies demyelination.

Question 13

Components of the AP
Amplitude correlates with _________ integrity. Decreased amplitude could indicate an _________ lesion (if the amplitude is decreased both _________ and _________) or it can indicate a _________ block across the site of injury (if the amplitude is low distally and not proximally).

Answer 13

Components of the AP
Amplitude correlates with axonal integrity. Decreased amplitude could indicate an axonal lesion (if the amplitude is decreased both distally and proximally) or it can indicate a conduction block across the site of injury (if the amplitude is low distally and not proximally).

Question 14

TYPES OF NERVE INJURIES
Nerve injuries can be classified depending on whether there is injury to the _________, the _________, or both. Often, especially with trauma, the affected structures do not always fit into one category. It is the job of the electromyographer to diagnose and communicate the type of injury that exists, the severity, and the location.

Answer 14

TYPES OF NERVE INJURIES
Nerve injuries can be classified depending on whether there is injury to the axon, the myelin, or both. Often, especially with trauma, the affected structures do not always fit into one category. It is the job of the electromyographer to diagnose and communicate the type of injury that exists, the severity, and the location.

Question 15

TYPES OF NERVE INJURIES
Seddon proposed a classification of nerve injuries in 1943 that is still commonly used as it correlates well with electrophysiology:
Neurapraxia – defined as _________ _________. This type of nerve injury occurs in the peripheral nerve with minor contusion or compression. There is preservation of the axon; only the myelin is affected. The transmission of APs is interrupted for a brief period, but recovery is usually complete in days to weeks. Seddon proposed a classification of nerve injuries in 1943 that is still commonly used as it correlates well with electrophysiology.

Answer 15

TYPES OF NERVE INJURIES
Seddon proposed a classification of nerve injuries in 1943 that is still commonly used as it correlates well with electrophysiology:
Neurapraxia – defined as conduction block. This type of nerve injury occurs in the peripheral nerve with minor contusion or compression. There is preservation of the axon; only the myelin is affected. The transmission of APs is interrupted for a brief period, but recovery is usually complete in days to weeks. Seddon proposed a classification of nerve injuries in 1943 that is still commonly used as it correlates well with electrophysiology.

Question 16

TYPES OF NERVE INJURIES
Axonotmesis – more significant injury: breakdown of _________ with accompanying _________ degeneration distal to the lesion. There is preservation of some of the supporting connective tissue stroma (Schwann cells and endoneurial tubes). Regeneration of axons (through collateral sprouting or axonal growth) can occur with good functional recovery, depending on the amount of axonal loss.

Answer 16

TYPES OF NERVE INJURIES
Axonotmesis – more significant injury: breakdown of axon with accompanying Wallerian degeneration distal to the lesion. There is preservation of some of the supporting connective tissue stroma (Schwann cells and endoneurial tubes). Regeneration of axons (through collateral sprouting or axonal growth) can occur with good functional recovery, depending on the amount of axonal loss.

Question 17

TYPES OF NERVE INJURIES
Neurotmesis – severe injury with complete _________ of the nerve and its supporting structures; extensive _________ or crush injury. The myelin, axon, perineurium, and epineurium are all disrupted. Spontaneous recovery is not expected.

Answer 17

TYPES OF NERVE INJURIES
Neurotmesis – severe injury with complete severance of the nerve and its supporting structures; extensive avulsing or crush injury. The myelin, axon, perineurium, and epineurium are all disrupted. Spontaneous recovery is not expected.

Question 18

TYPES OF NERVE INJURIES
Injury to the myelin can be _________ (local), _________ (throughout the nerve), or _________ (affecting some parts of the nerve but not others):
Uniform demyelination – slowing of CV along the entire nerve (e.g., _________-_________-_________ disease).

Answer 18

TYPES OF NERVE INJURIES
Injury to the myelin can be focal (local), uniform (throughout the nerve), or segmental (affecting some parts of the nerve but not others):
Uniform demyelination – slowing of CV along the entire nerve (e.g., Charcot-Marie-Tooth disease).

Question 19

TYPES OF NERVE INJURIES
Segmental demyelination – uneven degree of demyelination in different areas along the course of the nerve; may have variable slowing (_________ _________).

Answer 19

TYPES OF NERVE INJURIES
Segmental demyelination – uneven degree of demyelination in different areas along the course of the nerve; may have variable slowing (temporal dispersion).

Question 20

TYPES OF NERVE INJURIES
Focal nerve slowing – localized area of demyelination causing nerve _________; decreased CV is noted across the lesion.

Answer 20

TYPES OF NERVE INJURIES
Focal nerve slowing – localized area of demyelination causing nerve slowing; decreased CV is noted across the lesion.

Question 21

TYPES OF NERVE INJURIES
Conduction block – severe focal demyelination that prevents propagation of the AP through the area. There will be more than _________% amplitude decrement when the nerve is stimulated _________ to the lesion. The _________ CMAP amplitude remains intact. Clinically, conduction block presents as weakness.

Answer 21

TYPES OF NERVE INJURIES
Conduction block – severe focal demyelination that prevents propagation of the AP through the area. There will be more than 20% amplitude decrement when the nerve is stimulated proximal to the lesion. The distal CMAP amplitude remains intact. Clinically, conduction block presents as weakness.

Question 22

TYPES OF NERVE INJURIES
Axonal injuries will lead to _________ degeneration distal to the lesion. Low-amplitude CMAPs will be noted with both proximal and distal stimulation. On EMG, abnormal spontaneous potentials (fibrillations [fibs] and positive sharp waves [PSWs]) are seen. The MU recruitment will be decreased (_________ firing frequency of existing MUs). With reinnervation, MUs may become _________ with _________ amplitude and _________ duration.

Answer 22

TYPES OF NERVE INJURIES
Axonal injuries will lead to Wallerian degeneration distal to the lesion. Low-amplitude CMAPs will be noted with both proximal and distal stimulation. On EMG, abnormal spontaneous potentials (fibrillations [fibs] and positive sharp waves [PSWs]) are seen. The MU recruitment will be decreased (increased firing frequency of existing MUs). With reinnervation, MUs may become polyphasic with high amplitude and long duration.

Question 23

H-REFLEX
The H-reflex (Hoffmann reflex) is a _________ reflex and is the electrical equivalent of the _________ or oligosynaptic stretch reflex. It is a sensitive but nonspecific tool for possible S1 radiculopathy, especially when clinical, radiologic, and electrophysiologic signs of motor root involvement are lacking. In some cases, it may be the only abnormal study.

Answer 23

H-REFLEX
The H-reflex (Hoffmann reflex) is a true reflex and is the electrical equivalent of the monosynaptic or oligosynaptic stretch reflex. It is a sensitive but nonspecific tool for possible S1 radiculopathy, especially when clinical, radiologic, and electrophysiologic signs of motor root involvement are lacking. In some cases, it may be the only abnormal study.

Question 24

H-REFLEX
The H-reflex is usually elicited by _________ stimulating the _________ nerve in the _________ fossa. Such stimulation can be initiated by using slow (less than 1 pulse/s), long-duration (0.5 to 1 ms) stimuli with gradually increasing stimulation strength. The stimulus will travel along the most excitable _________ afferent nerve fibers, through the dorsal root ganglion (DRG). It then gets transmitted across the central synapse to the anterior horn cell, which then sends it down along the alpha motor axon to the muscle. Hence, the H-reflex is a measure of the time it takes for the orthodromic sensory response to get to the spinal cord proximally and the orthodromic motor response to reach the muscle distally (on which the recording electrode is placed).

Answer 24

H-REFLEX
The H-reflex is usually elicited by submaximally stimulating the tibial nerve in the popliteal fossa. Such stimulation can be initiated by using slow (less than 1 pulse/s), long-duration (0.5 to 1 ms) stimuli with gradually increasing stimulation strength. The stimulus will travel along the most excitable Ia afferent nerve fibers, through the dorsal root ganglion (DRG). It then gets transmitted across the central synapse to the anterior horn cell, which then sends it down along the alpha motor axon to the muscle. Hence, the H-reflex is a measure of the time it takes for the orthodromic sensory response to get to the spinal cord proximally and the orthodromic motor response to reach the muscle distally (on which the recording electrode is placed).

Question 25

H-REFLEX A generally acceptable result would be a motor response usually between _________ and _________ mV in amplitude and a latency of _________ to _________ ms. H-reflex studies are usually performed bilaterally because asymmetry of responses is an important criterion for abnormality. An abnormal latency greater than _________ to _________ ms (as compared with the other side) or H-reflex absence in patients under 60 years may suggest a lesion along the H-reflex pathway (afferent and/ or efferent fibers). This may be due to an S1 radiculopathy. The standard formula for calculating the H-reflex is 9.14 + 0.46 (leg length in cm from the medial malleolus to the popliteal fossa) + 0.1 (age). For a patient older than 60 years, _________ ms will be added to the total calculated value.

Answer 25

H-REFLEX A generally acceptable result would be a motor response usually between 0.5 and 5 mV in amplitude and a latency of 28 to 30 ms. H-reflex studies are usually performed bilaterally because asymmetry of responses is an important criterion for abnormality. An abnormal latency greater than 0.5 to 1.0 ms (as compared with the other side) or H-reflex absence in patients under 60 years may suggest a lesion along the H-reflex pathway (afferent and/ or efferent fibers). This may be due to an S1 radiculopathy. The standard formula for calculating the H-reflex is 9.14 + 0.46 (leg length in cm from the medial malleolus to the popliteal fossa) + 0.1 (age). For a patient older than 60 years, 1.8 ms will be added to the total calculated value.

Question 26

H-REFLEX In normal infants or adults with UMN (corticospinal tract) lesions, the H-reflex may be elicited in muscles other than the gastrocnemius/soleus muscles or flexor carpi radialis. It is often absent in patients older than _________ years. The reflex can be potentially inhibited by _________ muscle contractions and initiated by agonist muscle contractions.

Answer 26

H-REFLEX In normal infants or adults with UMN (corticospinal tract) lesions, the H-reflex may be elicited in muscles other than the gastrocnemius/soleus muscles or flexor carpi radialis. It is often absent in patients older than 60 years. The reflex can be potentially inhibited by antagonist muscle contractions and initiated by agonist muscle contractions.

Question 27

H-REFLEX The H-reflex does have some limitations. It is unable to distinguish between acute and chronic lesions, may be normal with _________ lesions, is diluted by _________ lesions, and is nonspecific in terms of injury location. Once the H-reflex is found to be abnormal, it will usually remain so, even with resolution of symptoms.

Answer 27

H-REFLEX The H-reflex does have some limitations. It is unable to distinguish between acute and chronic lesions, may be normal with incomplete lesions, is diluted by focal lesions, and is nonspecific in terms of injury location. Once the H-reflex is found to be abnormal, it will usually remain so, even with resolution of symptoms.

Question 28

F WAVES F wave or F response is a _________-amplitude, _________-latency _________ motor response that occurs following the activation of motor nerves. It derives its name from the word “foot” because it was first recorded from the intrinsic foot muscles. Unlike the H-reflex, the F wave does not represent a true reflex because there is no synapse from an afferent impulse to a motor nerve. Depolarizing peripheral nerves with external stimuli evokes potentials propagating both proximally and distally. Electrical stimulation of a peripheral nerve results in an _________ CMAP. In addition, the proximally (antidromically) propagating potential activates a small percentage of anterior horn motor neurons. In turn, this generates an orthodromic motor response (the F wave) along the same axon that activates a few muscle fibers picked up by the recording electrode.

Answer 28

F WAVES F wave or F response is a small-amplitude, variable-latency late motor response that occurs following the activation of motor nerves. It derives its name from the word “foot” because it was first recorded from the intrinsic foot muscles. Unlike the H-reflex, the F wave does not represent a true reflex because there is no synapse from an afferent impulse to a motor nerve. Depolarizing peripheral nerves with external stimuli evokes potentials propagating both proximally and distally. Electrical stimulation of a peripheral nerve results in an orthodromic CMAP. In addition, the proximally (antidromically) propagating potential activates a small percentage of anterior horn motor neurons. In turn, this generates an orthodromic motor response (the F wave) along the same axon that activates a few muscle fibers picked up by the recording electrode.

Question 29

F WAVES F waves can be obtained from any muscle by a _________ stimulus. Because of their variability (as opposed to H-reflexes), multiple stimulations must be used to obtain the _________ latency.

Answer 29

F WAVES F waves can be obtained from any muscle by a supramaximal stimulus. Because of their variability (as opposed to H-reflexes), multiple stimulations must be used to obtain the shortest latency.

Question 30

F WAVES F waves may be useful in the evaluation of _________ neuropathies with predominantly _________ involvement, such as _________-_________ syndrome and chronic inflammatory demyelinating polyneuropathies, in which distal conduction velocities may be _________ early in the disease.

Answer 30

F WAVES F waves may be useful in the evaluation of peripheral neuropathies with predominantly proximal involvement, such as Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathies, in which distal conduction velocities may be normal early in the disease.

Question 31

F WAVES However, the value of the F wave in evaluating focal nerve lesions, such as radiculopathy or peripheral nerve entrapment, is extremely limited largely due to the _________ of F-wave responses. In addition, most muscles receive innervation from multiple roots, so the fastest (nonaffected) fibers will be normal, as well as the fact that the results are nonspecific. It is a pure motor response, and its long neural pathway dilutes focal lesions and hinders the specificity of injury location. F waves are also generally not seen in nerves where the CMAP amplitude is severely reduced, such as severe axonal loss, since the F-wave amplitude is only 1% to 5% of the amplitude of the CMAP.

Answer 31

F WAVES However, the value of the F wave in evaluating focal nerve lesions, such as radiculopathy or peripheral nerve entrapment, is extremely limited largely due to the variability of F-wave responses. In addition, most muscles receive innervation from multiple roots, so the fastest (nonaffected) fibers will be normal, as well as the fact that the results are nonspecific. It is a pure motor response, and its long neural pathway dilutes focal lesions and hinders the specificity of injury location. F waves are also generally not seen in nerves where the CMAP amplitude is severely reduced, such as severe axonal loss, since the F-wave amplitude is only 1% to 5% of the amplitude of the CMAP.

Question 32

F WAVES Normal latency of F wave: upper limb: 28 ms; lower limb: 56 ms. Side-to-side difference:

Answer 32

F WAVES Normal latency of F wave: upper limb: 28 ms; lower limb: 56 ms. Side-to-side difference: <4.0 ms for lower limbs.

Question 33

Blink Reflex The most complicated of the late responses is the blink reflex. It is the electrophysiologic correlate of the _________ reflex. The sensory afferent limb of the reflex is the _________ nerve, a branch of the ophthalmic division of the _________ nerve (CN _________). Intervening synapses (_________ and _________) are stimulated. The motor efferent limb is the _________ nerve (CN _________), which innervates the _________ _________ muscle. As with the corneal reflex, stimulation of one side of the supraorbital branch of the trigeminal nerve elicits a motor response (eye blink) bilaterally through the facial nerves. Abnormalities anywhere along the reflex arc (central or peripheral) can be detected.

Answer 33

Blink Reflex The most complicated of the late responses is the blink reflex. It is the electrophysiologic correlate of the corneal reflex. The sensory afferent limb of the reflex is the supraorbital nerve, a branch of the ophthalmic division of the trigeminal nerve (CN V1). Intervening synapses (pons and medulla) are stimulated. The motor efferent limb is the facial nerve (CN VII), which innervates the orbicularis oculi muscle. As with the corneal reflex, stimulation of one side of the supraorbital branch of the trigeminal nerve elicits a motor response (eye blink) bilaterally through the facial nerves. Abnormalities anywhere along the reflex arc (central or peripheral) can be detected.

Question 34

Blink Reflex There is an early response (R1) due to a _________ reflex arc from the _________ sensory nucleus of V to the _________ facial nerve. There is also a late response (R2) due to multiple interneurons connecting the _________ sensory nucleus of V to the _________ spinal motor nucleus of V and then to the _________ facial nuclei.

Answer 34

Blink Reflex There is an early response (R1) due to a disynaptic reflex arc from the ipsilateral sensory nucleus of V to the ipsilateral facial nerve. There is also a late response (R2) due to multiple interneurons connecting the ipsilateral sensory nucleus of V to the ipsilateral spinal motor nucleus of V and then to the bilateral facial nuclei.

Question 35

Blink Reflex Recording electrodes are placed below and slightly lateral to the _________ bilaterally. Reference electrodes are placed just lateral to the lateral _________ bilaterally. The ground can be placed on the _________. The stimulator is placed over the medial supraorbital ridge of the _________. The sweep speed should be 5 or 10 ms with initial sensitivity of 100 or 200 μV.

Answer 35

Blink Reflex Recording electrodes are placed below and slightly lateral to the pupils bilaterally. Reference electrodes are placed just lateral to the lateral canthus bilaterally. The ground can be placed on the chin. The stimulator is placed over the medial supraorbital ridge of the eyebrow. The sweep speed should be 5 or 10 ms with initial sensitivity of 100 or 200 μV.

Question 36

Blink Reflex Normal latency for R1 response is <7 ms (Table 17-1).

Answer 36

Blink Reflex Normal latency for R1 response is <7 ms (Table 17-1).

Question 37

EMG INCLUDING MONOPOLAR VERSUS CONCENTRIC NEEDLE EMG testing involves evaluation of the electrical activity of skeletal or voluntary muscles. Muscles contract and produce movement through the orderly recruitment of MUs. An MU is defined as one _________ _________ cell, its _________, and all the _________ fibers innervated by that motor neuron. An MU is the fundamental structure that is assessed in EMG testing. EMG requires a thorough knowledge of the anatomy of the muscle being tested in order to place the needle electrode in the appropriate muscle.

Answer 37

EMG INCLUDING MONOPOLAR VERSUS CONCENTRIC NEEDLE EMG testing involves evaluation of the electrical activity of skeletal or voluntary muscles. Muscles contract and produce movement through the orderly recruitment of MUs. An MU is defined as one anterior horn cell, its axon, and all the muscle fibers innervated by that motor neuron. An MU is the fundamental structure that is assessed in EMG testing. EMG requires a thorough knowledge of the anatomy of the muscle being tested in order to place the needle electrode in the appropriate muscle.

Question 38

EMG INCLUDING MONOPOLAR VERSUS CONCENTRIC NEEDLE Monopolar needles are 22G to 30G Teflon-coated stainless steel needles with an exposed tip of 0.15 to 0.2 mm2 (Fig. 17-1A). They require a _________ electrode or a second needle as a _________ lead. Another surface electrode serves as a _________. A monopolar needle records the voltage changes between the tip of the electrode and the reference. Since it picks up from a full 360° field around the needle, it registers _________ amplitude and has increased _________ when compared with the concentric needle. The smaller diameter and the Teflon coat make the monopolar needle less uncomfortable. This, combined with its cost advantage over the concentric, has led to its preferential clinical use.

Answer 38

EMG INCLUDING MONOPOLAR VERSUS CONCENTRIC NEEDLE Monopolar needles are 22G to 30G Teflon-coated stainless steel needles with an exposed tip of 0.15 to 0.2 mm2 (Fig. 17-1A). They require a surface electrode or a second needle as a reference lead. Another surface electrode serves as a ground. A monopolar needle records the voltage changes between the tip of the electrode and the reference. Since it picks up from a full _________° field around the needle, it registers larger amplitude and has increased polyphasicity when compared with the concentric needle. The smaller diameter and the Teflon coat make the monopolar needle less uncomfortable. This, combined with its cost advantage over the concentric, has led to its preferential clinical use.

Question 39

EMG INCLUDING MONOPOLAR VERSUS CONCENTRIC NEEDLE Concentric needles are 24G to 26G stainless steel needles (Fig. 17-1B). The needle comprises a reference (_________) electrode with a bare inner wire in the center of the shaft that is the recording electrode. The concentric needle can register the voltage changes between the wire and the shaft. The pointed tip of the needle has an oval (_________) shape. Since the exposed active recording electrode is on the beveled portion of the cannula, the concentric needle picks up from a _________° field. Therefore, it registers _________ amplitude (since it has a _________ recording area). A separate surface electrode serves as the ground.

Answer 39

EMG INCLUDING MONOPOLAR VERSUS CONCENTRIC NEEDLE Concentric needles are 24G to 26G stainless steel needles (Fig. 17-1B). The needle comprises a reference (cannula) electrode with a bare inner wire in the center of the shaft that is the recording electrode. The concentric needle can register the voltage changes between the wire and the shaft. The pointed tip of the needle has an oval (beveled) shape. Since the exposed active recording electrode is on the beveled portion of the cannula, the concentric needle picks up from a 180° field. Therefore, it registers smaller amplitude (since it has a smaller recording area). A separate surface electrode serves as the ground.

Question 40

EFFECTS OF TEMPERATURE AND AGE ON NCS Cooling is thought to prolong the opening of Na+ channels. Decreasing the temperature of a limb affects SNAPs and CMAPs by _________ latency, _________ CV, and _________ amplitude and duration. CV _________ 2.4 m/s per 1° C decrease. Correction formulas exist but the best approach is to warm the limb prior to the NCS (32° in the upper limbs and 30° in the lower limbs).

Answer 40

EFFECTS OF TEMPERATURE AND AGE ON NCS Cooling is thought to prolong the opening of Na+ channels. Decreasing the temperature of a limb affects SNAPs and CMAPs by prolonging latency, decreasing CV, and increasing amplitude and duration. CV decreases 2.4 m/s per 1° C decrease. Correction formulas exist but the best approach is to warm the limb prior to the NCS (32° in the upper limbs and 30° in the lower limbs).

Question 41

EFFECTS OF TEMPERATURE AND AGE ON NCS As patients age, SNAP and CMAP amplitudes _________ and latencies _________. Motor NCSs for newborns are 50% of adult values since myelination is incomplete. Normal adult values are attained by age _________ years. After age _________ years, there is a progressive decline of 1 to 2 m/s per decade in the NCS of the fastest motor fibers.

Answer 41

EFFECTS OF TEMPERATURE AND AGE ON NCS As patients age, SNAP and CMAP amplitudes decrease and latencies increase. Motor NCSs for newborns are 50% of adult values since myelination is incomplete. Normal adult values are attained by age 5 years. After age 60 years, there is a progressive decline of 1 to 2 m/s per decade in the NCS of the fastest motor fibers.

Question 42

THE NEEDLE EMG EXAMINATION The EMG evaluation typically has four components: _________ activity. Activity at _________. _________ analysis. _________.

Answer 42

THE NEEDLE EMG EXAMINATION The EMG evaluation typically has four components: Insertional activity. Activity at rest. MU analysis. Recruitment.

Question 43

Insertional Activity Healthy muscle is electrically silent at rest. Insertional activity refers to the brief electrical activity associated with the needle entering the _________, which causes muscle fiber injury. The associated sound should be crisp.

Answer 43

Insertional Activity Healthy muscle is electrically silent at rest. Insertional activity refers to the brief electrical activity associated with the needle entering the sarcolemma, which causes muscle fiber injury. The associated sound should be crisp.

Question 44

Insertional Activity Insertional activity is classified in three ways: Normal insertional activity only lasts a few hundred milliseconds and is due to muscle _________.

Answer 44

Insertional Activity Insertional activity is classified in three ways: Normal insertional activity only lasts a few hundred milliseconds and is due to muscle depolarization.

Question 45

Insertional Activity Increased insertional activity occurs due to denervation or cell membrane _________ and lasts > _________ ms. There may be evidence of initially positive deflection waveforms that do not persist. If these positive waveforms are sustained and fire regularly, they are considered abnormal spontaneous potentials (see below).

Answer 45

Insertional Activity Increased insertional activity occurs due to denervation or cell membrane irritability and lasts >300 ms. There may be evidence of initially positive deflection waveforms that do not persist. If these positive waveforms are sustained and fire regularly, they are considered abnormal spontaneous potentials (see below).

Question 46

Insertional Activity Decreased insertional activity occurs when the needle is placed into _________ muscle, _________, or _________ and lasts

Answer 46

Insertional Activity Decreased insertional activity occurs when the needle is placed into atrophied muscle, fat, or edema and lasts <300 m/s.

Question 47

Activity at Rest NORMAL SPONTANEOUS ACTIVITY A needle should be inserted into a muscle at three to four different depths and in three to four different _________ (examining three or four electrically discrete areas of muscle) for insertional activity and activity at rest. The needle can be withdrawn almost to the skin and then redirected in a different direction, again stopping at three or four different _________. This can be repeated so that the needle examines about 12 to 16 discrete areas of the muscle (depending on the patient's tolerance).

Answer 47

Activity at Rest NORMAL SPONTANEOUS ACTIVITY A needle should be inserted into a muscle at three to four different depths and in three to four different directions (examining three or four electrically discrete areas of muscle) for insertional activity and activity at rest. The needle can be withdrawn almost to the skin and then redirected in a different direction, again stopping at three or four different depths. This can be repeated so that the needle examines about 12 to 16 discrete areas of the muscle (depending on the patient's tolerance).

Question 48

NORMAL SPONTANEOUS ACTIVITY After insertion of the needle into normal muscle at rest, there should be electrical _________ (Fig. 17-2A).

Answer 48

NORMAL SPONTANEOUS ACTIVITY After insertion of the needle into normal muscle at rest, there should be electrical silence (Fig. 17-2A).

Question 49

NORMAL SPONTANEOUS ACTIVITY Normal muscle may also display end plate activity. This occurs after a needle is placed in the region of the _________ or _________ _________. The needle should be moved out of the end plate, as the clinician cannot get reliable information about the muscle. Either of two waveforms may occur: miniature end plate potentials (MEPPs) or end plate potentials (EPPs). The patient may complain of increased pain. It is important to recognize these potentials so that they are not misinterpreted as abnormal spontaneous potentials.

Answer 49

NORMAL SPONTANEOUS ACTIVITY Normal muscle may also display end plate activity. This occurs after a needle is placed in the region of the NMJ or end plate. The needle should be moved out of the end plate, as the clinician cannot get reliable information about the muscle. Either of two waveforms may occur: miniature end plate potentials (MEPPs) or end plate potentials (EPPs). The patient may complain of increased pain. It is important to recognize these potentials so that they are not misinterpreted as abnormal spontaneous potentials.

Question 50

NORMAL SPONTANEOUS ACTIVITY MEPPs – Represent spontaneous release of _________ _________ of acetylcholine (ACh) at the _________ terminal that manifests as end plate noise (Fig. 17-2B).

Answer 50

NORMAL SPONTANEOUS ACTIVITY MEPPs – Represent spontaneous release of single quantum of acetylcholine (ACh) at the presynaptic terminal that manifests as end plate noise (Fig. 17-2B).

Question 51

NORMAL SPONTANEOUS ACTIVITY EPPs or “end plate spikes” – Represent single muscle fiber _________ at the presynaptic terminal with resultant release of large amounts of _________ (Fig. 17-2C). MEPPs and EPPs may or may not be present together (Fig. 17-2D).

Answer 51

NORMAL SPONTANEOUS ACTIVITY EPPs or “end plate spikes” – Represent single muscle fiber depolarizations at the presynaptic terminal with resultant release of large amounts of ACh (Fig. 17-2C). MEPPs and EPPs may or may not be present together (Fig. 17-2D).

Question 52

ABNORMAL SPONTANEOUS ACTIVITY Usually represents pathology (injury or denervation) that stems from a _________ or _________. These spontaneous depolarizations have an abnormal morphology and firing pattern.

Answer 52

ABNORMAL SPONTANEOUS ACTIVITY Usually represents pathology (injury or denervation) that stems from a muscle or nerve. These spontaneous depolarizations have an abnormal morphology and firing pattern.

Question 53

ABNORMAL SPONTANEOUS ACTIVITY Examples of muscle fiber–generated spontaneous potentials: _________ triphasic with initial positive (_________) deflection, PSWs biphasic with positive deflection, myotonic discharges, and complex repetitive discharges (CRDs).

Answer 53

ABNORMAL SPONTANEOUS ACTIVITY Examples of muscle fiber–generated spontaneous potentials: Fibs triphasic with initial positive (downward) deflection, PSWs biphasic with positive deflection, myotonic discharges, and complex repetitive discharges (CRDs).

Question 54

ABNORMAL SPONTANEOUS ACTIVITY Examples of neural-generated spontaneous potentials: _________ discharges, _________, _________ discharges, tremors, fasciculations, and multiple MU potentials.

Answer 54

ABNORMAL SPONTANEOUS ACTIVITY Examples of neural-generated spontaneous potentials: Myokymic discharges, cramps, neuromyotonic discharges, tremors, fasciculations, and multiple MU potentials.

Question 55

ABNORMAL SPONTANEOUS ACTIVITY Fibs and PSWs appear _________ weeks or more after injury.

Answer 55

ABNORMAL SPONTANEOUS ACTIVITY Fibs and PSWs appear 3 weeks or more after injury.

Question 56

ABNORMAL SPONTANEOUS ACTIVITY Abnormal spontaneous potentials are usually of _________ amplitude. Therefore, the gain on the EMG machine should be set to _________ to _________ μV for the best visualization (Fig. 17-3).

Answer 56

ABNORMAL SPONTANEOUS ACTIVITY Abnormal spontaneous potentials are usually of small amplitude. Therefore, the gain on the EMG machine should be set to 50 to 100 μV for the best visualization (Fig. 17-3).

Question 57

ABNORMAL SPONTANEOUS ACTIVITY Grading of fibs and PSWs is from 0 to 4+, with a sweep of _________ ms/division. (0) no fibs or PSWs present. (1+) _________ fib/PSW per screen persistent within two areas. (2+) fibs/PSWs in greater than _________ areas, about _________ per screen. (3+) fibs/PSWs in most muscle regions, greater than _________ of the screen. (4+) fibs/PSWs in all areas of the muscle and fill the _________ screen.

Answer 57

ABNORMAL SPONTANEOUS ACTIVITY Grading of fibs and PSWs is from 0 to 4+, with a sweep of 10 ms/division. (0) no fibs or PSWs present. (1+) one fib/PSW per screen persistent within two areas. (2+) fibs/PSWs in greater than two areas, about two per screen. (3+) fibs/PSWs in most muscle regions, greater than half of the screen. (4+) fibs/PSWs in all areas of the muscle and fill the entire screen.

Question 58

ABNORMAL SPONTANEOUS ACTIVITY Fasciculation potentials originate from a single MU and may have an intermittent or a normal firing pattern. When associated with PSWs or fibs, they suggest pathology. In the absence of fibs or PSWs, they may be due to _________, _________, or _________ (Fig. 17-4).

Answer 58

ABNORMAL SPONTANEOUS ACTIVITY Fasciculation potentials originate from a single MU and may have an intermittent or a normal firing pattern. When associated with PSWs or fibs, they suggest pathology. In the absence of fibs or PSWs, they may be due to stress, fatigue, or caffeine (Fig. 17-4).

Question 59

ABNORMAL SPONTANEOUS ACTIVITY CRDs frequently result from denervation and reinnervation through _________ _________. Their presence suggests a chronic process such as chronic radiculopathy, peripheral neuropathy, anterior horn disease, _________, or _________. (Fig. 17-5).

Answer 59

ABNORMAL SPONTANEOUS ACTIVITY CRDs frequently result from denervation and reinnervation through collateral sprouting. Their presence suggests a chronic process such as chronic radiculopathy, peripheral neuropathy, anterior horn disease, polymyositis, or myxedema. (Fig. 17-5).

Question 60

ABNORMAL SPONTANEOUS ACTIVITY Myotonic discharges (Fig. 17-6) originate in the muscle due to membrane instability. They have a characteristic _________ and _________ character and have been compared with a dive-bomber sound. They are commonly seen in myotonic dystrophy, myotonia congenita, polymyositis, chronic radiculopathy, peripheral neuropathy, _________ deficiency, and _________ periodic paralysis (Table 17-2).

Answer 60

ABNORMAL SPONTANEOUS ACTIVITY Myotonic discharges (Fig. 17-6) originate in the muscle due to membrane instability. They have a characteristic waxing and waning character and have been compared with a dive-bomber sound. They are commonly seen in myotonic dystrophy, myotonia congenita, polymyositis, chronic radiculopathy, peripheral neuropathy, maltase deficiency, and hyperkalemic periodic paralysis (Table 17-2).

Question 61

MU Analysis After analysis of insertional activity and spontaneous activity, the next step is to analyze the motor unit action potentials (MUAPs). First assess the morphology (_________, _________, _________, and _________ time). This should be done during a minimal contraction (sometimes positioning changes can bring this on). A trigger and delay line can be helpful in assessing MU stability.

Answer 61

MU Analysis After analysis of insertional activity and spontaneous activity, the next step is to analyze the motor unit action potentials (MUAPs). First assess the morphology (duration, amplitude, phases, and rise time). This should be done during a minimal contraction (sometimes positioning changes can bring this on). A trigger and delay line can be helpful in assessing MU stability.

Question 62

MU Analysis An MU is defined as an individual motor neuron, the muscle fibers it innervates (ranging from five to hundreds), and the NMJs between these two components. MUAP morphology varies depending on the _________ of the patient and the _________ being tested.

Answer 62

MU Analysis An MU is defined as an individual motor neuron, the muscle fibers it innervates (ranging from five to hundreds), and the NMJs between these two components. MUAP morphology varies depending on the age of the patient and the muscle being tested.

Question 63

MU Analysis Duration is measured from the initial deflection from the baseline to the return to baseline (typically 5 to 15 ms) and reflects the _________ of muscle fibers firing. The duration is increased with asynchronous firing of the fibers of an MU (as in reinnervation or other neuropathic processes) and is decreased in myopathic processes (fewer fibers contribute to the MU). When listening to the MUs, duration correlates with _________; thus, long duration is _________ and _________ and short duration is _________ and staticlike.

Answer 63

MU Analysis Duration is measured from the initial deflection from the baseline to the return to baseline (typically 5 to 15 ms) and reflects the synchrony of muscle fibers firing. The duration is increased with asynchronous firing of the fibers of an MU (as in reinnervation or other neuropathic processes) and is decreased in myopathic processes (fewer fibers contribute to the MU). When listening to the MUs, duration correlates with pitch; thus, long duration is dull and thuddy and short duration is crisp and staticlike.

Question 64

MU Analysis Amplitude is measured from the most positive to the most negative peak of the MU and reflects fiber density. The criteria for normal amplitude depend on the type of needle used (several hundred microvolts to a few millivolts for concentric needles, 1 to 7 μV for a monopolar needle). Amplitude increases (1) as the needle _________ the MU, (2) as the number of muscle fibers of the MU is _________, (3) with _________ diameter of the muscle fibers (muscle fiber hypertrophy), and (4) with more _________ firing of the muscle fibers. Also, amplitude may be increased after reinnervation (neuropathic injuries) and may be decreased in myopathies. When listening to the MUs, amplitude correlates with volume (not pitch).

Answer 64

MU Analysis Amplitude is measured from the most positive to the most negative peak of the MU and reflects fiber density. The criteria for normal amplitude depend on the type of needle used (several hundred microvolts to a few millivolts for concentric needles, 1 to 7 μV for a monopolar needle). Amplitude increases (1) as the needle approximates the MU, (2) as the number of muscle fibers of the MU is increased, (3) with increasing diameter of the muscle fibers (muscle fiber hypertrophy), and (4) with more synchronous firing of the muscle fibers. Also, amplitude may be increased after reinnervation (neuropathic injuries) and may be decreased in myopathies. When listening to the MUs, amplitude correlates with volume (not pitch).

Question 65

MU Analysis Phases are determined by counting the number of baseline crossings and adding _________. Polyphasia implies asynchronous firing of muscle fibers within an MU. Polyphasia is nonspecific and can be seen in both neuropathic and myopathic lesions. The MUAP is generally 2 to 4 phases. All muscles will normally exhibit about 10% polyphasia except the deltoid (up to 25% is normal). When listening to the MUs, polyphasia results in a clicking sound.

Answer 65

MU Analysis Phases are determined by counting the number of baseline crossings and adding one. Polyphasia implies asynchronous firing of muscle fibers within an MU. Polyphasia is nonspecific and can be seen in both neuropathic and myopathic lesions. The MUAP is generally 2 to 4 phases. All muscles will normally exhibit about 10% polyphasia except the deltoid (up to 25% is normal). When listening to the MUs, polyphasia results in a clicking sound.

Question 66

MU Analysis _________ (or turns) are defined as changes in the direction of a potential that do not cross baseline. Serrations also imply _________ firing of muscle fibers within an MU. Often serrations will become phases with a slight movement of the needle.

Answer 66

MU Analysis Serrations (or turns) are defined as changes in the direction of a potential that do not cross baseline. Serrations also imply asynchronous firing of muscle fibers within an MU. Often serrations will become phases with a slight movement of the needle.

Question 67

MU Analysis Satellite potentials are seen only after _________ has occurred. Satellite potentials appear after _________ _________ from adjacent intact MUs. The new sprouts are _________ and conduct slower than the original MU. As the reinnervation matures and myelinates, the satellite potential moves toward the MUAP until it eventually becomes an additional phase of the MUAP (these may require a trigger and delay line to be appreciated).

Answer 67

MU Analysis Satellite potentials are seen only after denervation has occurred. Satellite potentials appear after collateral sprouting from adjacent intact MUs. The new sprouts are unmyelinated and conduct slower than the original MU. As the reinnervation matures and myelinates, the satellite potential moves toward the MUAP until it eventually becomes an additional phase of the MUAP (these may require a trigger and delay line to be appreciated).

Question 68

MU Analysis Rise time is measured from the initial _________ deflection to the first _________ peak. It correlates with the _________ of the recording electrode to the MUAP being measured; thus, as the discharging MU is approached, the sound will become sharper. The electromyographer's qualitative analysis will be more accurate the closer they are to the MU. An acceptable rise time is 0.5 ms or less.

Answer 68

MU Analysis Rise time is measured from the initial positive deflection to the first negative peak. It correlates with the proximity of the recording electrode to the MUAP being measured; thus, as the discharging MU is approached, the sound will become sharper. The electromyographer's qualitative analysis will be more accurate the closer they are to the MU. An acceptable rise time is 0.5 ms or less.

Question 69

MU Analysis Stability – the morphology of an MU is stable in normal MUAPs. Unstable MUAP morphology (changes in amplitude or number of phases) occurs in primary _________ disorders and disorders associated with new or immature _________ (reinnervation). A trigger and delay function on the EMG machine may be helpful here.

Answer 69

MU Analysis Stability – the morphology of an MU is stable in normal MUAPs. Unstable MUAP morphology (changes in amplitude or number of phases) occurs in primary NMJ disorders and disorders associated with new or immature NMJs (reinnervation). A trigger and delay function on the EMG machine may be helpful here.

Question 70

Recruitment MUAPs normally fire in a semirhythmic pattern with a slight variation in the time between each MUAP. There are two ways to increase force during a muscle contraction: _________ the MU firing rate or _________ more MUs. Normally, one MU fires semirhythmically around 5 Hz. If more force is needed, that unit increases its firing rate (activation) and a second unit is recruited.

Answer 70

Recruitment MUAPs normally fire in a semirhythmic pattern with a slight variation in the time between each MUAP. There are two ways to increase force during a muscle contraction: increase the MU firing rate or recruit more MUs. Normally, one MU fires semirhythmically around 5 Hz. If more force is needed, that unit increases its firing rate (activation) and a second unit is recruited.

Question 71

Recruitment Most MUs will fire at about 10 Hz before recruiting a second MU. _________ recruitment usually occurs in _________ disorders where the _________ is damaged. There are therefore fewer MUs available to fire. In order to increase the strength of a contraction, these MUs fire at a higher frequency. This is also described more accurately as an increase in MU firing frequency.

Answer 71

Recruitment Most MUs will fire at about 10 Hz before recruiting a second MU. Decreased recruitment usually occurs in neuropathic disorders where the nerve is damaged. There are therefore fewer MUs available to fire. In order to increase the strength of a contraction, these MUs fire at a higher frequency. This is also described more accurately as an increase in MU firing frequency.

Question 72

Recruitment _________ or _________ recruitment usually occurs in _________ processes with a loss of _________ fibers. In order to increase the strength of a contraction, the remaining muscle fibers are quickly recruited. Many MUAPs are activated with minimal contraction. It is important not to confuse decreased recruitment (increased firing frequency of the MUs as seen in a neuropathic process) with early recruitment (recruitment of many MUAPs with slight contraction as seen in a myopathic process).

Answer 72

Recruitment Early or increased recruitment usually occurs in myopathic processes with a loss of muscle fibers. In order to increase the strength of a contraction, the remaining muscle fibers are quickly recruited. Many MUAPs are activated with minimal contraction. It is important not to confuse decreased recruitment (increased firing frequency of the MUs as seen in a neuropathic process) with early recruitment (recruitment of many MUAPs with slight contraction as seen in a myopathic process).

Question 73

Recruitment As a rule of thumb, myopathic MUAPs have _________ recruitment of _________ duration with _________ amplitude and an _________ firing rate. Neuropathic MUAPs have late recruitment of increased duration and increased amplitude. MUAPs of CNS disorders have normal morphology, but may have a decreased activation.

Answer 73

Recruitment As a rule of thumb, myopathic MUAPs have early recruitment of short duration with low amplitude and an increased firing rate. Neuropathic MUAPs have late recruitment of increased duration and increased amplitude. MUAPs of CNS disorders have normal morphology, but may have a decreased activation.

Question 74

Median Neuropathy at the Wrist (carpal tunnel syndrome) Median neuropathy at the wrist presents with a combination of signs/symptoms known as carpal tunnel syndrome (CTS) – the most _________ entrapment neuropathy. Etiologies are multifactorial with varying contributions of local and systemic factors. The initial presentation is usually due to a demyelinating lesion of the median nerve sensory fibers. Demyelination may also affect the motor fibers early on. This may progress to axonal loss of both sensory and motor fibers.

Answer 74

Median Neuropathy at the Wrist (carpal tunnel syndrome) Median neuropathy at the wrist presents with a combination of signs/symptoms known as carpal tunnel syndrome (CTS) – the most common entrapment neuropathy. Etiologies are multifactorial with varying contributions of local and systemic factors. The initial presentation is usually due to a demyelinating lesion of the median nerve sensory fibers. Demyelination may also affect the motor fibers early on. This may progress to axonal loss of both sensory and motor fibers.

Question 75

Median Neuropathy at the Wrist (carpal tunnel syndrome) Patient presentation is the most important aspect of the clinical diagnosis of CTS. The symptoms include numbness, tingling, and pain along the median nerve distribution (palmar surface of the first 3½ digits). Symptoms may be worst or most prevalent at _________ and may wake the patient from sleep. Weakness of grip strength (inability to open jars or dropping objects) may occur as symptoms progress and median motor fibers become involved. CTS can be bilateral, but the dominant hand is usually affected first.

Answer 75

Median Neuropathy at the Wrist (carpal tunnel syndrome) Patient presentation is the most important aspect of the clinical diagnosis of CTS. The symptoms include numbness, tingling, and pain along the median nerve distribution (palmar surface of the first 3½ digits). Symptoms may be worst or most prevalent at night and may wake the patient from sleep. Weakness of grip strength (inability to open jars or dropping objects) may occur as symptoms progress and median motor fibers become involved. CTS can be bilateral, but the dominant hand is usually affected first.

Question 76

Median Neuropathy at the Wrist (carpal tunnel syndrome) Physical examination involves sensory test (pin prick, 2-point discrimination, and/or Semmes-Weinstein pressure mono-filaments) and motor test/inspection for _________ _________ _________ (_________) atrophy and weakness. The special/provocative tests may assist in diagnosis (Table 17-3). The affected side should always be compared with the nonaffected side.

Answer 76

Median Neuropathy at the Wrist (carpal tunnel syndrome) Physical examination involves sensory test (pin prick, 2-point discrimination, and/or Semmes-Weinstein pressure mono-filaments) and motor test/inspection for abductor pollicis brevis (APB) atrophy and weakness. The special/provocative tests may assist in diagnosis (Table 17-3). The affected side should always be compared with the nonaffected side.

Question 77

Median Neuropathy at the Wrist (carpal tunnel syndrome) Electrodiagnostic studies are helpful in confirming the diagnosis of CTS (_________% to _________% sensitivity) and determining the type of lesion (demyelinating, axonal, or both). However, one must keep in mind that all those with abnormal studies do not necessarily have CTS and all those with CTS do not necessarily have abnormal studies.

Answer 77

Median Neuropathy at the Wrist (carpal tunnel syndrome) Electrodiagnostic studies are helpful in confirming the diagnosis of CTS (85% to 90% sensitivity) and determining the type of lesion (demyelinating, axonal, or both). However, one must keep in mind that all those with abnormal studies do not necessarily have CTS and all those with CTS do not necessarily have abnormal studies.

Question 78

Median Neuropathy at the Wrist (carpal tunnel syndrome) Classic evaluation of CTS includes motor and sensory NCS of median nerve and its comparison with the ulnar nerve (ipsilaterally) and median nerve (contralaterally). A needle study may be helpful to assess for axonal damage or reinnervation and to rule out radiculopathy or other nerve lesions. _________ SNAPs are recorded with the active electrode over the _________ interphalangeal (_________) joint of the second or third digit and stimulating the mid-palm (7 cm from electrode) and across the carpal tunnel (14 cm from electrode). Note: larger/smaller distances can be used depending on the size of the patient's hand – it is important to change the distance in your recordings, as this will affect the velocity.

Answer 78

Median Neuropathy at the Wrist (carpal tunnel syndrome) Classic evaluation of CTS includes motor and sensory NCS of median nerve and its comparison with the ulnar nerve (ipsilaterally) and median nerve (contralaterally). A needle study may be helpful to assess for axonal damage or reinnervation and to rule out radiculopathy or other nerve lesions. Antidromic SNAPs are recorded with the active electrode over the proximal interphalangeal (PIP) joint of the second or third digit and stimulating the mid-palm (7 cm from electrode) and across the carpal tunnel (14 cm from electrode). Note: larger/smaller distances can be used depending on the size of the patient's hand – it is important to change the distance in your recordings, as this will affect the velocity.

Question 79

Median Neuropathy at the Wrist (carpal tunnel syndrome) The electrodiagnostic analysis of CTS depends upon evidence of median nerve slowing, conduction block, or axon loss in the carpal tunnel. Commonly used criteria include prolonged absolute motor or sensory _________, sensory slowing across the carpal tunnel (or relatively prolonged or slowed in comparison with other nerves or the contralateral median nerve) as well as amplitude changes that would indicate axonal loss or a conduction block.

Answer 79

Median Neuropathy at the Wrist (carpal tunnel syndrome) The electrodiagnostic analysis of CTS depends upon evidence of median nerve slowing, conduction block, or axon loss in the carpal tunnel. Commonly used criteria include prolonged absolute motor or sensory latency, sensory slowing across the carpal tunnel (or relatively prolonged or slowed in comparison with other nerves or the contralateral median nerve) as well as amplitude changes that would indicate axonal loss or a conduction block.

Question 80

Median Neuropathy at the Wrist (carpal tunnel syndrome) Sensory changes that may indicate CTS (note that all findings must be taken in the context of the global findings in all nerves): – CV _________ ms compared with the ipsilateral ulnar nerve – amplitude of the median response across the carpal tunnel

Answer 80

Median Neuropathy at the Wrist (carpal tunnel syndrome) Sensory changes that may indicate CTS (note that all findings must be taken in the context of the global findings in all nerves): – CV 0.5 ms compared with the ipsilateral ulnar nerve – amplitude of the median response across the carpal tunnel

Question 81

Median Neuropathy at the Wrist (carpal tunnel syndrome) Motor changes that may indicate CTS (sensory fibers are usually affected first): – latency of > _________ ms at a distance of _________ cm from the active electrode – latency of > _________ ms greater than the ipsilateral ulnar motor nerve latency

Answer 81

Median Neuropathy at the Wrist (carpal tunnel syndrome) Motor changes that may indicate CTS (sensory fibers are usually affected first): – latency of >4.2 ms at a distance of 8 cm from the active electrode – latency of >1 ms greater than the ipsilateral ulnar motor nerve latency

Question 82

Median Neuropathy at the Wrist (carpal tunnel syndrome) The EMG test should include the _________ muscle. If the _________ is abnormal (PSW/fibs), more proximal median as well as nonmedian innervated muscles should be tested to rule out a more proximal median neuropathy, peripheral neuropathy, plexopathy, radiculopathy, or a lesion of the anterior horn cell.

Answer 82

Median Neuropathy at the Wrist (carpal tunnel syndrome) The EMG test should include the APB muscle. If the APB is abnormal (PSW/fibs), more proximal median as well as nonmedian innervated muscles should be tested to rule out a more proximal median neuropathy, peripheral neuropathy, plexopathy, radiculopathy, or a lesion of the anterior horn cell.

Question 83

Median Neuropathy at the Wrist (carpal tunnel syndrome) A possible source of confusion in median nerve electrodiagnostic studies is a _________-_________ anastomosis. This relatively common anastomosis (found in 15% to 20% of population) occurs when ulnar fibers (destined for ulnar innervated muscles) travel with the median nerve at the elbow. In the forearm, the nerve fibers travel with the anterior interosseous nerve and cross over to join the ulnar nerve (median to ulnar anastamoses).

Answer 83

Median Neuropathy at the Wrist (carpal tunnel syndrome) A possible source of confusion in median nerve electrodiagnostic studies is a Martin-Gruber anastomosis. This relatively common anastomosis (found in 15% to 20% of population) occurs when ulnar fibers (destined for ulnar innervated muscles) travel with the median nerve at the elbow. In the forearm, the nerve fibers travel with the anterior interosseous nerve and cross over to join the ulnar nerve (median to ulnar anastamoses).

Question 84

Median Neuropathy at the Wrist (carpal tunnel syndrome) There are three classic electrodiagnostic findings: First: The median CMAP has a positive (_________) initial deflection after median nerve stimulation at the elbow that is not seen with wrist stimulation. This deflection occurs because ulnar fibers (traveling at the elbow with median nerve fibers, before joining the ulnar nerve in the forearm) arrive first and stimulate the adductor muscle of the thumb causing downward deflection to be recorded over the APB.

Answer 84

Median Neuropathy at the Wrist (carpal tunnel syndrome) There are three classic electrodiagnostic findings: First: The median CMAP has a positive (downward) initial deflection after median nerve stimulation at the elbow that is not seen with wrist stimulation. This deflection occurs because ulnar fibers (traveling at the elbow with median nerve fibers, before joining the ulnar nerve in the forearm) arrive first and stimulate the adductor muscle of the thumb causing downward deflection to be recorded over the APB.

Question 85

Median Neuropathy at the Wrist (carpal tunnel syndrome) There are three classic electrodiagnostic findings: Second: The CMAP amplitude of median nerve stimulation at the elbow will be _________ compared with the wrist stimulation. This can occur without median nerve entrapment. The amplitude is increased because at the elbow the ulnar nerve hitchhiking fibers are stimulated and added to the median CMAP, whereas at the wrist only median nerve fibers are stimulated and recorded.

Answer 85

Median Neuropathy at the Wrist (carpal tunnel syndrome) There are three classic electrodiagnostic findings: Second: The CMAP amplitude of median nerve stimulation at the elbow will be larger compared with the wrist stimulation. This can occur without median nerve entrapment. The amplitude is increased because at the elbow the ulnar nerve hitchhiking fibers are stimulated and added to the median CMAP, whereas at the wrist only median nerve fibers are stimulated and recorded.

Question 86

Median Neuropathy at the Wrist (carpal tunnel syndrome) There are three classic electrodiagnostic findings: Third: There may be a false _________ in median NCV in the forearm based on proximal (at the elbow) stimulation calculations. This is more prevalent in patients with CTS. Ulnar fibers stimulated with the median nerve at the elbow do not have to traverse the carpal tunnel and will therefore result in a faster proximal latency than normal.

Answer 86

Median Neuropathy at the Wrist (carpal tunnel syndrome) There are three classic electrodiagnostic findings: Third: There may be a false increase in median NCV in the forearm based on proximal (at the elbow) stimulation calculations. This is more prevalent in patients with CTS. Ulnar fibers stimulated with the median nerve at the elbow do not have to traverse the carpal tunnel and will therefore result in a faster proximal latency than normal.

Question 87

ULNAR NEUROPATHY AT THE ELBOW Ulnar neuropathy at the elbow (_________ tunnel syndrome) is the second most common mononeuropathy of the upper extremity (second only to CTS). Patients usually complain of sensory changes in the fourth and fifth digits and/or weakness of the hand.

Answer 87

ULNAR NEUROPATHY AT THE ELBOW Ulnar neuropathy at the elbow (cubital tunnel syndrome) is the second most common mononeuropathy of the upper extremity (second only to CTS). Patients usually complain of sensory changes in the fourth and fifth digits and/or weakness of the hand.

Question 88

ULNAR NEUROPATHY AT THE ELBOW Physical examination must include inspection for deformity and signs of muscle atrophy (_________ _________ interosseous and _________ _________ _________ [_________]), individual muscle strength testing, thorough sensory examination (including the dorsal ulnar cutaneous nerve), and special tests.

Answer 88

ULNAR NEUROPATHY AT THE ELBOW Physical examination must include inspection for deformity and signs of muscle atrophy (first dorsal interosseous and abductor digiti minimi [ADM]), individual muscle strength testing, thorough sensory examination (including the dorsal ulnar cutaneous nerve), and special tests.

Question 89

ULNAR NEUROPATHY AT THE ELBOW Tinel's sign occurs when mild taps at the _________ _________ or _________ tunnel cause numbness or paresthesia in the hand along the ulnar nerve distribution.

Answer 89

ULNAR NEUROPATHY AT THE ELBOW Tinel's sign occurs when mild taps at the ulnar groove or cubital tunnel cause numbness or paresthesia in the hand along the ulnar nerve distribution.

Question 90

ULNAR NEUROPATHY AT THE ELBOW Froment's sign occurs when the patient is asked to hold a piece of paper between thumb and index finger and there is flexion of the thumb at the _________ joint. The patient will substitute the _________ _________ _________ muscle (innervated by the _________ nerve) for the _________ _________ muscle (innervated by the ulnar nerve).

Answer 90

ULNAR NEUROPATHY AT THE ELBOW Froment's sign occurs when the patient is asked to hold a piece of paper between thumb and index finger and there is flexion of the thumb at the IP joint. The patient will substitute the flexor pollicis longus muscle (innervated by the median nerve) for the adductor pollicis muscle (innervated by the ulnar nerve).

Question 91

ULNAR NEUROPATHY AT THE ELBOW Electrodiagnostic studies may help pinpoint the site of compression of the ulnar nerve, prognosticate, and distinguish ulnar neuropathy at the elbow from other pathologies. Depending on the severity, SNAPs may be affected, resulting in decreased amplitude. A side-to-side difference of more than _________% is considered significant.

Answer 91

ULNAR NEUROPATHY AT THE ELBOW Electrodiagnostic studies may help pinpoint the site of compression of the ulnar nerve, prognosticate, and distinguish ulnar neuropathy at the elbow from other pathologies. Depending on the severity, SNAPs may be affected, resulting in decreased amplitude. A side-to-side difference of more than 50% is considered significant.

Question 92

ULNAR NEUROPATHY AT THE ELBOW The _________ _________ _________ nerve should be tested in suspected ulnar neuropathy at the elbow. This cutaneous nerve takes off just before the ulnar nerve enters _________ canal, which helps distinguish between ulnar neuropathy at _________ canal (the _________ _________ _________ response will be normal) and that more proximally. If CMAPs are decreased and the SNAPs are normal, consider cervical radiculopathy.

Answer 92

ULNAR NEUROPATHY AT THE ELBOW The dorsal ulnar cutaneous nerve should be tested in suspected ulnar neuropathy at the elbow. This cutaneous nerve takes off just before the ulnar nerve enters Guyon's canal, which helps distinguish between ulnar neuropathy at Guyon's canal (the dorsal ulnar cutaneous response will be normal) and that more proximally. If CMAPs are decreased and the SNAPs are normal, consider cervical radiculopathy.

Question 93

ULNAR NEUROPATHY AT THE ELBOW Slowing of the ulnar motor response across the elbow may be noted. Slowing of more than _________ m/s (compared with distal CV) is considered significant. If the elbow is not flexed (90° to 135°), the CV may be falsely _________. The length of the segment should be measured by following the path of the nerve with the elbow bent. An amplitude drop of more than _________% to _________% compared with the distal segment may indicate conduction block. The “inching technique” (stimulating at _________-cm intervals and assessing for a drop in amplitude or excessive latency) can further help localize the site of entrapment.

Answer 93

ULNAR NEUROPATHY AT THE ELBOW Slowing of the ulnar motor response across the elbow may be noted. Slowing of more than 10 m/s (compared with distal CV) is considered significant. If the elbow is not flexed (90° to 135°), the CV may be falsely decreased. The length of the segment should be measured by following the path of the nerve with the elbow bent. An amplitude drop of more than 20% to 30% compared with the distal segment may indicate conduction block. The “inching technique” (stimulating at 1-cm intervals and assessing for a drop in amplitude or excessive latency) can further help localize the site of entrapment.

Question 94

ULNAR NEUROPATHY AT THE ELBOW Needle EMG testing can be difficult to interpret. Because the innervation of the _________ _________ _________ (_________) sometimes occurs proximal and sometimes distal to the elbow, it is frequently spared in ulnar neuropathy at the elbow. NCS (including evaluation of the _________ _________ _________ nerve) must be taken into consideration when making a diagnosis.

Answer 94

ULNAR NEUROPATHY AT THE ELBOW Needle EMG testing can be difficult to interpret. Because the innervation of the flexor carpi ulnaris (FCU) sometimes occurs proximal and sometimes distal to the elbow, it is frequently spared in ulnar neuropathy at the elbow. NCS (including evaluation of the dorsal ulnar cutaneous nerve) must be taken into consideration when making a diagnosis.

Question 95

PERONEAL NEUROPATHY The common peroneal nerve (also known as the _________ nerve) gives off a branch to the _________ head of _________ _________ that then proceeds to wind around the fibular head/neck where it becomes very superficial. This is the main site of entrapment of the common peroneal nerve, which then courses into the fibular tunnel and divides into superficial and deep pero-neal nerves. The etiology of compression is usually trauma, habituation, iatrogenic, or work related. The pathophysiology can present as myelin, axon, or mixed damage, based on severity and etiology of compression. The clinical presentation is usually foot drop (_________ gait with inability to _________) and paresthesia/numbness on the _________ of the foot and _________ leg.

Answer 95

PERONEAL NEUROPATHY The common peroneal nerve (also known as the fibular nerve) gives off a branch to the short head of biceps femoris that then proceeds to wind around the fibular head/neck where it becomes very superficial. This is the main site of entrapment of the common peroneal nerve, which then courses into the fibular tunnel and divides into superficial and deep pero-neal nerves. The etiology of compression is usually trauma, habituation, iatrogenic, or work related. The pathophysiology can present as myelin, axon, or mixed damage, based on severity and etiology of compression. The clinical presentation is usually foot drop (steppage gait with inability to dorsiflex) and paresthesia/numbness on the dorsum of the foot and lateral leg.

Question 96

PERONEAL NEUROPATHY The electrodiagnostic study remains the best test to assess the degree of nerve damage and pinpoint the location of entrapment. The classic NCS includes a sensory study of the bilateral superficial peroneal nerves and a motor study of the peroneal nerves with recording electrode at _________ _________ _________ (_________; _________ ant _________ erior muscle can be used as the recording electrode if the _________ is atrophied).

Answer 96

PERONEAL NEUROPATHY The electrodiagnostic study remains the best test to assess the degree of nerve damage and pinpoint the location of entrapment. The classic NCS includes a sensory study of the bilateral superficial peroneal nerves and a motor study of the peroneal nerves with recording electrode at extensor digitorum brevis (EDB; tibialis anterior muscle can be used as the recording electrode if the EDB is atrophied).

Question 97

PERONEAL NEUROPATHY The motor studies are performed with stimulation at the _________, below the _________ head, and in the _________ popliteal fossa. These findings should be compared with the contralateral side. In general, a lower extremity motor CV of

Answer 97

PERONEAL NEUROPATHY The motor studies are performed with stimulation at the ankle, below the fibular head, and in the lateral popliteal fossa. These findings should be compared with the contralateral side. In general, a lower extremity motor CV of

Question 98

PERONEAL NEUROPATHY An accessory peroneal nerve should be suspected if the peroneal CMAP is larger on _________ (fibular head) stimulation than on _________ (ankle) stimulation. This anomalous innervation can be found by stimulating _________ to the lateral malleolus. The amplitude of the CMAP stimulating at the ankle plus the amplitude of the CMAP stimulating posterior to the lateral malleolus will approximate the CMAP amplitude stimulating over the fibular head. Needle EMG helps confirm axonal loss, assess the degree of involvement of the muscles innervated by the pero-neal nerve, localize the lesion, and rule out L5 radiculopathy/plexopathy. The examination of the short head of the biceps femoris muscle is very important, as this is the only peroneal nerve–innervated muscle above the knee. If this muscle demonstrates abnormality, the lesion is proximal to the fibular head.

Answer 98

PERONEAL NEUROPATHY An accessory peroneal nerve should be suspected if the peroneal CMAP is larger on proximal (fibular head) stimulation than on distal (ankle) stimulation. This anomalous innervation can be found by stimulating posterior to the lateral malleolus. The amplitude of the CMAP stimulating at the ankle plus the amplitude of the CMAP stimulating posterior to the lateral malleolus will approximate the CMAP amplitude stimulating over the fibular head. Needle EMG helps confirm axonal loss, assess the degree of involvement of the muscles innervated by the pero-neal nerve, localize the lesion, and rule out L5 radiculopathy/plexopathy. The examination of the short head of the biceps femoris muscle is very important, as this is the only peroneal nerve–innervated muscle above the knee. If this muscle demonstrates abnormality, the lesion is proximal to the fibular head.