Chapter 17 Electrodiagnostics Flashcards
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.
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.
Electrodiagnostic studies:
Indications for electrodiagnostic testing include _________, tingling/_________, pain, weakness, atrophy, depressed deep tendon reflexes, and/or fatigue.
Electrodiagnostic studies:
Indications for electrodiagnostic testing include numbness, tingling/paresthesias, pain, weakness, atrophy, depressed deep tendon reflexes, and/or fatigue.
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.
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.
INITIAL SETTINGS FOR NCS
- _________ 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).
- Motor settings: sweep – 2 ms/division, gain – 5 mV/division.
- Sensory settings: sweep – 2 ms/division, gain – 20 μV/division.
INITIAL SETTINGS FOR NCS
- 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).
- Motor settings: sweep – 2 ms/division, gain – 5 mV/division.
- Sensory settings: sweep – 2 ms/division, gain – 20 μV/division.
INITIAL SETTINGS FOR EMG
- Sweep speed: _________ ms/division
- Low-frequency filter: _________ to _________ Hz
- High-frequency filter: _________ to _________ Hz
- Amplifier sensitivity: _________ to _________ μV
INITIAL SETTINGS FOR EMG
- Sweep speed: 10 ms/division
- Low-frequency filter: 10 to 30 Hz
- High-frequency filter: 10,000 to 20,000 Hz
- Amplifier sensitivity: 50 to 100 μV
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.
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.
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 _________.
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.
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.
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.
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.
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.
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).
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).
Components of the AP
Latency measurement requires standardized and accurately recorded _________ or else the results are meaningless.
Components of the AP
Latency measurement requires standardized and accurately recorded distance or else the results are meaningless.
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.
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.
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).
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).
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.
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.
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.
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.
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.
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.
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.
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.
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).
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).
TYPES OF NERVE INJURIES
Segmental demyelination – uneven degree of demyelination in different areas along the course of the nerve; may have variable slowing (_________ _________).
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).
TYPES OF NERVE INJURIES
Focal nerve slowing – localized area of demyelination causing nerve _________; decreased CV is noted across the lesion.
TYPES OF NERVE INJURIES
Focal nerve slowing – localized area of demyelination causing nerve slowing; decreased CV is noted across the lesion.
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.
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.
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.
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.
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.
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.
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).
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
F WAVES
Normal latency of F wave: upper limb: 28 ms; lower limb: 56 ms. Side-to-side difference: <_________ ms for lower limbs.
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.
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.
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.
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.
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.
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.
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.
Blink Reflex
Normal latency for R1 response is <7 ms (Table 17-1).
Blink Reflex
Normal latency for R1 response is <7 ms (Table 17-1).
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.
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.
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.
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.
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.
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.