PMR 3 - EMG Flashcards
Assuming correct timing of performing the complete neurodiagnostic study, which of the following conditions would most likely result in a normal EMG/NCS test?
a. Bell’s palsy
b. Brachial plexopathy (e.g., medial cord)
c. Botulism
d. Myofascial pain
e. Ulnar nerve impingement at elbow
D) Myofascial pain does not lead to changes in the nerves or muscles that are quantifiable by electrodiagnostic testing. In general, changes to the sensory or motor nerve (axonal, demyelinating, or both), the neuromuscular junction, or the muscle itself can lead to electrophysiological changes that can be quantifiable by electrodiagnostic testing.
The amplitude of the compound motor action potential (CMAP) you have obtained is very small, and you are unable to assess where the takeoff is. In order to see the takeoff more clearly, you should:
a. Increase the sweep speed
b. Decrease the sweep speed
c. Increase the gain
d. Decrease the gain
C) Increasing the gain is equal to increasing the sensitivity. By increasing the gain from 1,000 microvolts (1 millivolt)/division to 500 microvolts/division, each “box” on the Y-axis will portray a smaller percentage of the waveform. If the CMAP amplitude is 2,000 microvolts in amplitude, and if the gain is 1,000 microvolts (1 millivolt)/division, the waveform will be two boxes high. If the gain is increased to 500 microvolts/division, the waveform will be four boxes tall (hence amplified). The sweep speed is represented on the X-axis and is measured in milliseconds/division.
The most common error in the realm of neurodiagnostic testing is typically related to which of the following?
a. Computer analysis failure
b. Excessive ambient temperature/room temperature
c. Lack of repeat calibration of the testing probe with each measurement
d. Operator error
e. Patient’s inability to fully relax
D) Of all of the possible mistakes that can lead to false-positive or false-negative electrodiagnostic results, the most common one is due to the person performing the test.
These include not performing the test correctly, not interpreting the test correctly, not testing the appropriate nerves or muscles, failing to account for anomalous innervation, improper technique, or performing the test too early (before findings would be apparent on neurodiagnostic testing).
Which of the following does the nerve conduction component of the a, neurodiagnostic study fail to assess or give information about?
a. Autonomic nerve
b. Integrity of myelin
c. Motor nerve
d. Sensory nerve
e. Speed of transmission
A) Except for somatosensory evoked potentials, electrodiagnostic testing only assesses the peripheral nervous system.
Testing is possible of both the motor and the sensory fibers. Assessment can be made about the integrity of the myoneural junction, the axon, and the myelin. However, the autonomic nervous system is not evaluated by conventional nerve studies and EMG.
Which of the following has the poorest prognosis of nerve recovery?
a. Axonomesis
b. Conduction block
c. Demyelination
d. Neurapraxia
e. Neurotmesis
E) Neurotmesis is a complete disruption of the axon, the myelin, and all supporting connective tissues. Complete nerve regeneration is unlikely, as there is no path for the nerve to follow when trying to connect to the distal muscles.
What is the most proximal muscle innervated by the common peroneal nerve?
a. Anterior tibialis
b. Short head of biceps femoris
c. Hamstring
d. Peroneus longus
B) The short head of the biceps femoris is the first (and only) muscle innervated by the common peroneal nerve. The sciatic nerve divides into the tibial and peroneal (also called the fibular) nerves in the posterior thigh. The only muscle innervated by the peroneal nerve proximal to the knee is the short head of the biceps femoris. Testing this muscle is important when a patient presents with foot drop or suspected peroneal nerve injury to localize the lesion. Abnormal spontaneous potentials (fibrillations and positive sharp waves) in the short head of the biceps femoris place the lesion at the common peroneal nerve in the thigh or more proximal. The tibial innervated muscles must also be examined, as the lesion may involve the sciatic nerve. The peroneal division of the sciatic nerve is often more affected than the tibial division
To determine whether an ulnar nerve lesion is at the wrist or the elbow, it is important to test:
a. Conduction velocity across the elbow
b. Needle testing of the first dorsal interosseous muscle
c. The dorsal ulnar cutaneous nerve
d. The ulnar motor response to the first dorsal interosseous muscle
C) The dorsal ulnar cutaneous nerve is a sensory branch of the ulnar nerve that supplies the dorsum of the hand. It can easily be obtained (and compared with the nonaffected hand). The dorsal ulnar cutaneous nerve branches above the wrist.
Therefore, in lesions at the wrist, the dorsal ulnar cutaneous nerve will be spared.
Decreased amplitude of the dorsal ulnar cutaneous nerve indicates that the ulnar nerve lesion is above the wrist.
Conduction block in the fore arm would present with:
a. Decreased compound motor action potential (CMAP) amplitude with proximal stimulation and distal stimulation
b. Decreased CMAP amplitude with proximal stimulation but not distal stimulation
c. Decreased CMAP amplitude distally but not proximally
d. Slowing of conduction velocity across the lesion
B) Conduction block is an area of focal demyelination that is so severe that the action potential cannot propagate. If the conduction block were located in the forearm, stimulation distal to the conduction block would be normal. When stimulation occurred across the area of conduction block, some of the action potentials could not propagate. This would lead to a drop in MAP amplitude (with proximal stimulation). D is incorrect because slowing of conduction velocity is actually the result of a conduction block with subsequent remyelination. The immature myelin conducts slower than normal myelin, leading to a slowing of conduction velocity.
Axonal damage (with Wallerian degeneration) would present with:
a. Decreased compound motor action potential (CAP) amplitude with proximal stimulation and distal stimulation
b. Decreased CMAP amplitude with proximal stimulation but not distal stimulation
c. Decreased MAP amplitude distally but not proximally
d. Slowing of conduction velocity across the lesion
e. Slowing of conduction velocity distal to the lesion
A) Wallerian degeneration occurs distal to the level of an axonal injury. Since with MAP stimulation the pickup is always over a distal muscle, both proximal and distal stimulation would result in decreased CMAP amplitude.
What is the clinical manifestation of conduction block?
a. Weakness
b. There is no clinical manifestation
c. Rash
d. Atrophy
A) Conduction block is an area of focal demyelination that is so severe that the action potential cannot propagate. This leads to a decreased number of motor units available to contribute to the strength of a contraction.
The prognosis is excellent once the offending mechanism (usually pressure on the nerve) has been removed. (For sensory fibers, the clinical manifestation would be sensory loss.)
Which of the following is not an indication that a Martin-Gruber anastomosis is present?
a. An initial positive deflection of the median compound motor action potential (CMAP) when
stimulating the median nerve at the antecubital fossa
b. Slowed median nerve conduction velocity in the forearm
c. Decreased amplitude of the median CMAP with distal stimulation as compared with proximal stimulation
d. An excessively fast median nerve forearm conduction velocity when carpal tunnel is present
B) Martin-Gruber anastomosis is a median to ulnar nerve anastomosis in the forearm.
Most commonly these are ulnar fibers that are destined for the ulnarly innervated hand muscles that travel with the median nerve proximally and then cross over to the ulnar nerve in the forearm (usually from the anterior interos seous nerve). When the active electrode is placed over the abductor pollicis brevis muscle (median nerve study), and the median nerve is stimulated at the antecubital fossa, the ulnarly innervated adductor pollicis muscle is stimulated as well (from the ulnar fibers that travel with the median nerve).
Remember, in the forearm, these fibers switch over to again travel with the ulnar nerve.
Because these fibers do not have to go through the carpal tunnel, the action potential reaches the adductor pollicis muscle before the median fibers get to the abductor pollicis brevis (APB) muscle. Therefore, there is an initial positive (downward) deflection with stimulation of the median nerve in the antecubital fossa (this occurs because the active electrode is not over the motor point of the muscle being activated, the active electrode is over the APB muscle, not the adductor motor point). There is decreased amplitude of the median CMAP with distal stimulation as compared with proximal stimulation because distal stimulation only activates the median innervated APB muscle.
Proximal stimulation activates the median innervated APB muscle as well as the nearby ulnar innervated adductor pollicis muscle.
The excessively fast median forearm conduction velocity noted with a Martin-Gruber anastomosis when carpal tunnel is present is due to the proximal stimulation of ulnar fi bers which do not have to travel through the carpal tunnel). This leads to a spuriously decreased latency with proximal stimulation compared with the increased latency of the distally stimulated median nerve.
During electrodiagnostic testing, how can you tell if an accessory peroneal nerve is present?
a. There is decreased compound motor action potential (CMAP) amplitude when the peroneal nerve is stimulated at the ankle and normal CMAP amplitude with stimulation at the fibular head
b. There is decreased MAP amplitude when the peroneal nerve is stimulated at the fibular head and normal CMAP amplitude with stimulation at the ankle
C. There is unusually slowed conduction velocity in the peroneal nerve
d. There is unusually fast conduction velocity in the peroneal nerve
A) An accessory peroneal nerve is a branch from the superficial peroneal nerve that travels posterior to the lateral malleolus and can innervate the lateral portion of the extensor digitorum brevis (EDB) muscle. The fibers from the accessory branch are not activated with ankle stimulation and therefore cannot contribute to the distal MAP amplitude. These fibers are activated with proximal stimulation. If the accessory branch is stimulated posterior to the lateral mallelus (with pickup on the EDB), a waveform will be obtained. Usually, this CMAP amplitude, when added to the CMAP amplitude of the ankle stimulation, will equal the CMAP amplitude of stimulation at the fibular head.
What is the only muscle that is innervated exclusively by the C5 nerve root?
a. Supraspinatus
b. Levator scapulae
c. Trapezius
d. Rhomboid (maior and minor)
D) The dorsal scapular nerve (which innervates the rhomboid muscle) is the first branch off the upper trunk and is usually composed of C5 fibers only.
When is it most appropriate to perform
F-waves?
a. For the evaluation of radiculopathy
b. For the evaluation of peroneal neuropathy at the fibular head
c. For the evaluation of possible acute inflammatory demyelinating polyneuropathy (AIDP)
d. For the evaluation of peripheral neuropathy
C) F-waves are low-amplitude late
responses thought to be due to antidromic activation of motor neurons. They have variable latency and configuration with variable responses. They are indicated to assess proximal conduction in conditions such as AIDP (also known as Guillain-Barré syndrome). F-waves are reported to be among the earliest electrodiagnostic findings in AIDP. F-waves should not be used routinely to assess for radiculopathy. The most commonly assessed parameter of F-waves is the shortest F latency. F-waves evaluate a very long neural pathway, are nonspecific, and can be affected by anything that would slow the pathway (i.e., peripheral neuropathy and focal slowing). The exact location of the slowing cannot be assessed, so to use an F-wave to say the slowing is at the root level is faulty. In addition, since the active electrode is over a muscle that would have multiple root innervations and since the F-wave onlv assesses the fastest fibers, in theory the F-wave should be normal in a radiculopathy.
Radiculopathies may affect the axon, and the F-wave is a test of latency. If there is slowing of the neural path in a radiculopathy, the area of slowing is small compared with the length of the pathway assessed with an F-wave.
Finally, since the F-wave latency is extremely variable, multiple stimulations must be performed to find the shortest latency. The number of stimulations, therefore, has to be high (more than 10) and even then, the electromyographer is never sure that the shortest latency has been recorded.
What is the difference between an unmyelinated nerve and a demyelinated nerve?
a. The location of the sodium channels
b. The resting transmembrane potential
C. The way the sodium-potassium pump operates
d. The ions that are required
A) A myelinated nerve has sodium channels located only at the nodes of Ranvier.
An unmyelinated nerve has sodium channels throughout the length of the nerve. Therefore, if a myelinated nerve loses its myelin (becomes demyelinated), the sodium channels are still located at distinct intervals throughout the nerve. If saltatory conduction cannot occur (because the myelin has been lost), the action potential cannot propagate along the nerve. Therefore, conduction block will occur. Conduction block does not occur in an unmyelinated nerve since the lesion in a conduction block is myelin.
Why should the elbow be bent to about
90 degrees when performing and measuring ulnar nerve stimulation across the elbow?
a. The ulnar nerve is not slack in that position and its length is more accurately estimated, so the conduction velocity will not be falsely slowed
b. The ulnar nerve is not taught in that position, so the conduction velocity will not be falsely slowed
C. The ulnar nerve is not slack in that position, so the conduction velocity will not be falsely increased
d. The ulnar nerve is not taught in that position, so the conduction velocity will not be falsely increased
A) The ulnar nerve is slack when the arm is extended. When the arm is bent, the ulnar nerve is no longer slack. The measurement should also be done in this position, following the path of the nerve. Since speed = distance/unit of time, a falsely low distance will falsely slow the conduction velocity.
Which muscles are innervated, at least partially, by the L5 nerve root?
a. Peroneus longus, semimembranosus, vastus medialis
b. Adductor longus, gluteus medius, extensor digitorum longs
c. Tibialis anterior, adductor magnus, biceps femoris
d. Tibialis anterior, gluteus maximus, peroneus longus
D) All three of these muscles contain innervation from the L5 nerve root, although through different peripheral nerves. The tibialis anterior is from the deep peroneal nerve, the gluteus maximus from the inferior gluteal nerve, and the peroneus longus from the superficial peroneal nerve.
In a normal adult, from what muscle can an H-reflex be obtained?
a. Hamstring
b. Flexor carpi radialis
c. Biceps
d. Extensor digitorum
B) In normal adults, an H-reflex can be obtained in the flexor carpi radialis muscle and can therefore be useful in the assessment of C6/7 radiculopathies. In the normal adult, an H-reflex elicited in any muscle besides the gastrocnemius-soleus or the flexor carpi radialis is considered pathological and may indicate an upper motor neuron lesion.
In amyotrophic lateral sclerosis (ALS), the sensory nerve action potential
(SNAP) will be:
a. Normal
b. Decreased amplitude distally and proximally
c. Decreased amplitude distally
d. Increased
A) ALS is a disorder of the motor nerves.
As such, the motor fibers, but not the sensory fibers, would be affected. Therefore, the SNAPs should be normal, whereas the compound motor action potentials might show decreased amplitudes.
In myopathies, the motor unit action potentials (MUAPs) may demonstrate all of the following except:
a. Low amplitude
b. Long duration
c. Polyphasicity
d. Early recruitment
B) In myopathies, motor units usually have low amplitude (less than 1 millivolt when using a monopolar needle), short duration, polyphasicity, and early recruitment
Complex repetitive discharges (CRDs)
are most likelv seen in:
a. Radiculopathy of 4 weeks duration
b. Carpal tunnel syndrome of 1 year duration
c. Lumbar radiculopathy of 1 week duration
d. Sensory axonal peripheral neuropathy of 2 years duration
B) CRDs are usually noted in longstanding disorders (more than 6 months old). They represent groups of spontaneously firing action potentials with an affected area of muscle electrically stimulating an adjacent muscle fiber. This produces a local muscular arrhythmia. The patterns repeat regularly with a frequency of 10 to 100 Hz. They have the sound of a motorboat misfiring. They can be seen in chronic neurogenic or myopathic disorders. Since the needle study would be normal in a sensory neuropathy (only the motor fibers are tested with needle testing), CRDs would not be noted in a sensory peripheral neuropathy.
The normal gain for a sensory nerve study is:
a. 100 microvolts/division
b. 1,000 microvolts (1 millivolt)/division
c. 10 millivolts/division
d. 20 microvolts/division
D) The gain is the Y-axis on the screen.
Normal sensory nerve amplitudes are between 10 and 20 microvolts/division. If the gain is set too low, the SNAP will be merely a blip on the screen (oscilloscope). (Remember that gain means sensitivity. A low gain would be 1,000 microvolts/division or 1 millivolt/division.) Compound motor action potentials, which have an amplitude of about 5 millivolts, can be visualized on a gain of 1 millivolt/division.
The X-axis on the oscilloscope (screen)
represents:
a. Time in microseconds
b. Time in milliseconds
c. Distance in centimeters
d. Distance in millimeters
B) The X-axis (sweep) represents time, which is usually in milliseconds per division.
When determining the location and extent of a peroneal nerve lesion, an important nerve to include in the electrodiagnostic test is:
a. The lateral femoral cutaneous nerve
b. The superficial peroneal nerve
c. The lateral peroneal nerve
d. The medial peroneal nerve
B) Below the knee, the common peroneal nerve branches into the superficial and deep peroneal nerves. The superficial nerve innervates the peroneus longs and brevis and provides innervation to the lateral aspect of the lower leg as well as the dorsum of the foot (except for the first dorsal web space, which is innervated by the deep peroneal nerve). The superficial peroneal nerve is a sensory nerve that is easy to perform, but often omitted. Just like the dorsal ulnar cutaneous nerve, it can be helpful in determining location and severity of a lesion.
It should be noted that the peroneal nerve is also known as the fibular nerve
In a brachial plexopathy, the sensory nerve action potentials (SNAP):
a. Would be affected as the lesion is distal to the dorsal root ganglion
b. Would not be affected as the lesion is distal to the dorsal root ganglion
c. Would be affected as the lesion is proximal to the dorsal root ganglion
d. Would not be affected as the lesion is proximal to the dorsal root ganglion
A) In a brachial plexopathy, the lesion is distal to the sensory nerve body (the dorsal root ganglion). As such, the continuity between the cell body and the end organ has been affected. Therefore, the SNAP would be affected. Conversely, in a radicular lesion, there is continuity between the dorsal root ganglion and the end organ (the sensation over the hand or foot), so the SNAP is not affected.
When calculating a “normal” H-reflex, all of the following should be taken into consideration except:
a. Age
b. Height
c. Temperature
d. Latency on the opposite side
C) H-reflex represents the time in milliseconds for a stimulation from the popliteal fossa to travel orthodromically in afferent sensory fibers, synapse in the spinal cord, and then travel orthodromically in efferent motor fibers to a pick up over the gastrocnemius-soleus muscle. Of course, the taller the individual, the longer this pathway will take. In addition, nerves conduct slower as a person ages, so an older individual will likely have a longer latency. There are nomograms to correct for the H-reflex given a person’s age and height. Comparing the affected side with the nonaffected side is important. A side-to-side latency difference of more than 1.5 milliseconds is usually considered significant. Although temperature usually plays a role in latency and amplitude when testing peripheral nerves with a distal pickup, with an H-reflex the pickup is over a more proximal (and therefore warmer) muscle.
Therefore, the temperature is not usually a significant factor.
In an axonal injury, all of the following may be noted except:
a. Denervation in all muscles innervated by that nerve
b. Decreased compound motor action potential (CMAP) amplitude with distal stimulation
c. Decreased CMAP amplitude with proximal stimulation
d. Decreased sensory nerve action potential (SNAP) amplitude
A) In an axonal injury, Wallerian degeneration occurs distal to the nerve lesion, and therefore, enervation may be noted in all muscles distal to the area of injury. Muscles innervated by a particular nerve, but proximal to the level of the axonal injury, should not be affected. With nerve conduction studies, the pickup is over a distal muscle (which would have been innervated by a nerve that has undergone Wallerian degeneration). Therefore, with both distal and proximal stimulation, the CMAP amplitude may be decreased.
A lumbar plexopathy affecting the posterior division will affect all of the following muscles except:
a. Sartorius
b. Rectus femoris
c. Adductor longus
d. Pectineus
C) The adductor longs muscle is innervated by the obturator nerve, which comes off of the anterior division. The other muscles are innervated by the femoral nerve, which comes off of the posterior division.
To definitively state that a patient who presents for electrodiagnostic (EMG)
testing has a radiculopathy, the following must all be present except:
a. Denervation in two different muscles innervated by different peripheral nerves but the same nerve root
b. Normal sensory nerve action potentials (SNAPS)
c. An abnormal F-wave
d. Denervation in the corresponding paraspinal muscles
C) To definitively state that the patient has a radiculopathy, the findings must include denervation in the paraspinal muscles as well as denervation in two different muscles innervated by different peripheral nerves but the same nerve root. Because the lesion is preganglionic, the SNAPs should be normal.
Abnormal F waves are nonspecific and not helpful in the evaluation of a radiculopathy.
As opposed to acquired neuropathies, congenital neuropathies usually:
a. Have proximal more than distal slowina
b. Have uniform slowing throughout the nerve
c. Have segmental slowing throughout the nerve
d. Are distal
B) Congenital (hereditary) neuropathies usually have slowing throughout the entire course of the nerve. Acquired neuropathies are usually more distal or segmental.
Temporal dispersion is a feature of an acquired neuropathy.
Electrodiagnostic findings common in myopathies include:
a. Low amplitude sensory nerve action potentials (SNAP)
b. Long duration motor units
c. Abnormal spontaneous potentials (denervation) on needle EMG
d. Increased fi ring frequency of motor units
C) Denervation can be found in neuropathic or myopathic processes. Since myopathies only affect the muscle, SNAPs should be preserved. The motor units are usually short duration, small amplitude, polvphasic potentials with early recruitment.
In electrodiagnostic testing, increased fi ring frequency refers to:
a. A firing rate of more than 10 Hz before the next motor unit is recruited
b. Increased recruitment
c. A myopathic process
d. Fibrillations and positive sharp waves (PSWs)
A) An increased firing frequency is frequently reported as “decreased recruitment.” Both mean that a single motor unit fi res faster than normal before a second motor unit is recruited. Muscles can increase their strength in one of two ways; they can recruit more motor units, or the motor units that are there can fi re faster. In a neuropathic process, there are not more motor units that can be recruited. Therefore, the remaining motor units have to fire faster to increase the strength of the contraction. One motor unit may fire at 20 Hz (cycles per second) or faster. If the sweep is set at 10 milliseconds per division, and there are 10 divisions per screen, then the screen represents 1/10 of a second. Therefore, if a motor unit fires twice in a screen, it is fi ring at about 20 Hz.
What muscles would be affected in a C6 radiculopathy?
a. Extensor carpi radialis
b. Flexor digitorum superficialis
c. Extensor indicis
d. Rhomboid major
A) The extensor carpi radialis is innervated by the radial nerve C5/6. The flexor digitorum superficialis is via the median nerve
C7-T1. The extensor indicis is via the radial nerve C7/8. The rhomboid is innervated by the dorsal scapular nerve, C5.
What type of neuropathy is usually seen on electrodiagnostic testing in alcoholic neuropathy?
a. Axonal sensory neuropathy
b. Demyelinating sensory motor neuropathy
c. Axonal and demyelinating sensory motor neuropathy
d. Axonal sensory motor neuropathy
D) The peripheral neuropathy usually seen in alcoholic neuropathy is axonal sensory motor neuropathy. This means that low amplitudes would be seen in the sensory nerve action potentials (SNAPs) and compound motor action potentials (CAPs) with relative preservation of the velocities (up to 20% decrease in velocity can be seen, as the fastest fibers may be affected).
What type of neuropathy is usually seen on electrodiagnostic testing in diabetic neuropathy?
a. Axonal sensory neuropathy
b. Demyelinating sensory motor neuropathy
C. Axonal and demyelinating sensory motor neuropathy
d. Axonal sensory motor neuropathy
C) The peripheral neuropathy seen in diabetic neuropathy is usually axonal and demyelinating sensory motor neuropathy.
This means that low-amplitude sensory nerve action potentials (SNAPs) and compound motor action potentials (MAPs) would be noted with slowing of nerve conduction velocities (both sensory and motor) and increased latencies.
What type of neuropathy is usually seen on electrodiagnostic testing in paraneoplastic syndrome?
a. Axonal sensory neuropathy
b. Demyelinating sensory motor neuropathy
c. Axonal and demyelinating sensory motor neuropathy
d. Axonal sensory motor neuropathy
A) A patient who has low amplitude sensory nerve action potentials with preserved compound motor action potential amplitudes (and relatively normal conduction velocities and latencies) should be suspected of having a paraneoplastic syndrome.
During electrodiagnostic testing, motor unit analysis should be done:
a. With the muscle at rest
b. With a surface electrode
c. With minimal contraction
d. With maximum contraction
C) The patient should be asked to contract the muscle minimally so that only one or two motor units are noted on the screen. If there is maximal contraction, individual motor units will not be able to be evaluated (as they will
“run into” each other). In addition, it is important to note the recruitment frequency (i.e., how fast one motor unit is firing when another motor unit is recruited).
The best way to localize whether a lesion is in the plexus or a radiculopathy is:
a. Assess sensory nerve action potential (SNAP) amplitude
b. Look for enervation in the extremity muscles
c. Assess compound motor action potential (CMAP) amplitude
d. F-waves
A) If a lesion is in the plexus, it will be postganglionic (i.e., distal) to the dorsal root ganglion. Therefore, the SNAP amplitudes will be affected. If a lesion is at the root level, it will be preganglionic (i.e., proximal to the dorsal root ganglion). Therefore, the SNAP amplitudes will not be affected. In both cases, there mav be enervation in the extremitv muscles. In a radiculopathy, there may be denervation in the paraspinal muscles as well.
F-wave abnormalities are nonspecific and may indicate that the problem is between the stimulation point and the spinal cord. This would include both plexopathy and radiculopathy, and so does not distinguish between the two.
If it can be avoided, why should short distances not be used when measuring conduction velocities in electrodiagnostic testing?
a. They are not reproducible
b. They may not include the area of injury
C. You cannot use the measuring tape
d. The margin of error is larger
D) A 1-cm error in measurement over a 10-cm segment will lead to a 10% margin of error.
If a 5-cm segment is used, the margin of error becomes 20%.
In electrodiagnostic testing, a cold limb (less than 32 °C in the arms or 30°C in the legs) could lead to:
a. Decreased latency of compound motor action potentials (CAPs)
b. Increased amplitude of sensory nerve action potentials (SNAPs)
C.Increased conduction velocity of SNAPS
d. Decreased amplitude of CMAPs
B) It is better to warm a limb than use correction formulas. A limb that is cold may demonstrate increased latency, decreased conduction velocity, and increased amplitude of SNAPs and CMAPs. With cooling, the U latency is prolonged about 0.2 ms/degree centigrade, amplitude increases (sensory more than motor), conduction velocity decreases 1.8 to 2.4 meters/second/degree centigrade, and duration increases. This is presumed to be due to sodium channels taking longer to open, but staying open longer, with cooling.
Monopolar needles generally have higher amplitude motor unit action potentials 41. (MUAPs) than concentric needles because:
a. Monopolar needles are longer than concentric needles
b. The needle samples from 360 ‹ degrees rather than 180 degrees
c. The tip of a concentric needle is smaller
d. Concentric needles have the ground electrode as part of the needle
B) Concentric needles are beveled and therefore only pick up from 180 degrees
around the needle tip. Monopolar needles pick up electrical activity from 360 degrees.
Therefore, the MUAP amplitudes from a monopolar needle are usually larger than those from a concentric needle. It is important to include information about the type of needle in the report so that the amplitude can be interpreted correctly. Concentric needles have the reference electrode as part of the needle and require a separate ground.
When performing needle EMG with a monopolar needle, the best location for the reference electrode is:
a. Over nonmuscle distal to the needle
b. Over nonmuscle but close to the needle
c. Over a muscle innervated by the same nerve as the muscle you are testing
d. Over the same muscle and close to the needle
D) To decrease interference and make the baseline as quiet as possible, the reference electrode should be placed over the same muscle that is being tested. The EMG machine will “subtract” the electrical activity of the reference electrode, therefore getting rid of any excess noise.
In the newborn, nerve conduction velocities are approximately what percentage of adult values?
а. 50%
b. 25%
c. 100%
d. 75%
A) At birth, most of the myelination is incomplete. Conduction vélocities are about half of adult values. By 1 year of age, the velocity is about 75%. Myelination is usually complete by age 3 to 5.
All of the following can affect H-reflex latency on electrodiagnostic testing except:
a. Demyelinating sensory neuropathy
b. Demyelinating motor neuropathy
c. Height
d. Weight
D) A demyelinating neuropathy will slow nerves and therefore increase the latency of the H-reflex. Because the pathway of the H-reflex involves both sensory and motor fibers, either type of neuropathy will affect the H reflex. The height of the person will affect the H-reflex latency because the pathway is longer (it takes a longer time to travel a longer distance).
In electrodiagnostic testing, the ideal minimal distance between the active and the reference electrode in a sensory nerve study is:
a. 1 cm
b. 4 cm
c. 1 inch
d. 2 cm
B) There should be at least 4 cm between the active and the reference electrodes. If the electrodes are placed too close together, the sensory nerve action potential (SNAPS amplitude could falsely decrease (resembling an axonal lesion). This has to do with the rise time of the SNAP. The EMG machine will
“subtract” the recorded action potential of the reference electrode from the recorded action potential of the active electrode. If the action potential reaches the reference electrode during the rise time of the action potential seen by the active electrode, the EMG machine will subtract one from the other, resulting in a decreased SNAP amplitude.
When performing a needle EMG study, rise time of a motor unit action potential (MUAP) 46. refers to:
a. Time for a motor unit to fire
b. Time from baseline to initial negative peak
c. Time lag from the peak of the initial negative deflection to the subsequent positive (downward) peak
d. Time from the baseline takeoff to when the waveform returns to baseline
B) The rise time is measured as the time from the peak of the initial positive deflection to the subsequent negative upward peak. The rise time is used to estimate the distance between the recording tip and the discharging motor unit. If the needle is far from the muscle that is being activated, the rise time will be prolonged (more than 0.5 milliseconds) and the motor unit will sound duller or “thuddier.”
If this occurs, the needle should be repositioned. A distant motor unit will have a longer rise time because of the resistance and capacitance of the tissues that separate the needle from the activated muscle. This will act as a high-frequency filter.
Your patient has a distal median sensory conduction velocity of 65 m/sec and a proximal (across the carpal tunnel)
median sensory conduction velocity of 50 m/sec. This indicates:
a. Carpal tunnel syndrome
b. Normal findings
c. Peripheral neuropathy
d. Sensory carpal tunnel syndrome
D) Although 50 m/sec is considered a
“normal” conduction velocity, you must interpret the results in relation to the patient’s other nerves. If the distal sensory conduction velocity is greater than 10 m/sec more than the conduction velocity across the carpal tunnel, then a sensory carpal tunnel is presumed to exist. Note that sensory carpal tunnel is the correct answer and not carpal tunnel syndrome. It is important to be as descriptive as possible. Here, we do not know what the median motor latency is, so sensory carpal tunnel is more descriptive. In addition, nerves usually conduct slower the more distal they are. This is because they are thinner with less myelin and are more superficial (and therefore cooler- cooling slows down nerves). Findings in a peripheral neuropathy would be slower conduction in the distal segment rather than the proximal (across the carpal tunnel).
The anterior interosseous nerve innervates all of the following muscles except:
a. Flexor digitorum profundus to digits 2 and 3
b. Pronator quadratus
c. Flexor digitorum superficialis to digits 1 and 2
d. Flexor pollicis longus
C) The anterior interosseous nerve is a motor branch of the median nerve that innervates the flexor digitorum profundus to digits 2 and 3, the flexor pollicis longus, and the pronator quadratus. Its function can be tested by asking the patient to make the “OK” sign, which utilizes these muscles. When testing for anterior interosseous nerve injury, the nerve conduction studies are usually normal, as the active electrode is over the abductor pollicis brevis muscle. Needle MG findings of enervation limited to the three muscles listed above would be diagnostic of an AIN (anterior interosseous nerve) lesion.
If a patient has tarsal tunnel syndrome, one would likely find which of the following on nerve conduction studies?
a. Increased latency of the sural nerve at the ankle
b. Increased latency of the tibial nerve at the ankle
c. Decreased conduction velocity of the tibial nerve
d. Decreased conduction velocity of the peroneal (fibular) nerve
B) Tarsal tunnel syndrome is an entrapment neuropathy of the tibial nerve below the flexor retinaculum behind the medial malleolus. The most sensitive test is the mixed medial and lateral plantar nerves.
On needle MG testing, normal muscles at rest:
a. Are electrically silent
b. Will spontaneously discharge potentials with an initial negative deflection
c. Will spontaneously discharge potentials with an initial positive deflection
d. Will discharge potentials only if the muscle belly is tapped
A) Normal muscles at rest are electrically silent. Sticking a needle in a muscle will damage it, and a potential with an initial positive deflection may be noted. However, this potential does not persist. A muscle that has been damaged or enervated will spontaneously discharge potentials that have an initial positive (downward deflection and persist when the needle is not moving. Fibers with an initial negative (upward) potential most likely indicate incomplete relaxation.
Tapping over the muscle belly is not recommended as it serves no purpose, except perhaps to occasionally confuse the electromyographer when a waveform is seen as the needle is moved in the muscle.
The waveform below is most likely:
a. An end plate potential
b. A fibrillation potential
c. A positive sharp/wave
d. A motor unit
D) Although this waveform has an initial positive deflection, it is a motor unit. The gain is set at 1,000 microvolts (i.e., each box represents 1 millivolt). The waveform is much too large to be a fibrillation (fi b), a positive sharp wave (PSW), or an end plate potential, (which are usually seen when the gain is set at 100 microvolts/division). If it were a fib or PS, it would appear as a very small blip on the baseline.
The motor unit action potential below was taken using a monopolar needle in the quadriceps muscle. What can you determine about the amplitude of the motor unit?
a. Normal
b. Decreased amplitude
c. Increased amplitude
d. Mixed increased and decreased amplitude
B) The gain is set at 50 microvolts.
Therefore, the largest motor unit is 200 microvolts in amplitude. This is considered a small amplitude potential, as normal amplitude of a motor unit using a monopolar L needle is about 1 to 7 millivolts in amplitude.
In what condition might you see a potential such as this one?
a. Normal muscle
b. Myopathy
C. Neuropathy
d. Disorder of the neuromuscular junction
B) Small amplitude, short duration polyphasic motor units are often seen in myopathies. In chronic neuropathies, the motor units may be of large amplitude, long duration, and polyphasic.
