PMR 3 - EMG Flashcards

Question

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

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

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.

Answer 5

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.

Answer 6

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.

Answer 7

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.

Answer 8

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.

Answer 9

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.

Answer 10

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).

Answer 11

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.

Answer 12

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.

Answer 13

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).

Answer 14

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.

Answer 15

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%.

Answer 16

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.

Answer 17

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.

Answer 18

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.

Answer 19

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.

Answer 20

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).

Answer 21

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.

Answer 22

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.

Answer 23

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).

Answer 24

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.

Answer 25

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.

Answer 26

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.

Answer 27

D) Duration is the time from the initial baseline departure to the final return to baseline. Normal duration is about 5 to 15. milliseconds or approximately one horizontal division with a commonly used sweep speed of 10 msec/division. It represents the degree of synchrony in the fi ring of the individual motor fibers that contribute to the motor unit. With reinnervation, there is asynchrony of fi ring of individual muscle fibers due to immature myelin. Therefore, duration of a motor unit increases with reinnervation and can be seen in chronic neuropathic processes. Decreased duration may be seen in myopathic disorders.

Answer 28

C) Fibrillations and positive sharp waves are seen in acute processes (either neuropathic or myopathic). Polyphasicity and long duration motor units are noted with reinnervation and asynchronous firing of the individual muscle fibers that make up a motor unit. Complex repetitive discharges are noted in chronic processes as well.

Answer 29

C) The posterior cord includes the axillary nerve (to the deltoid) and the radial nerve (to the triceps and extensor indicis proprius). The pronator teres is innervated through the lateral cord and the median nerve.

Answer 30

D) Diabetes, pregnancy, thyroid disorders (as well as rheumatoid arthritis, edema, gout, and peripheral neuropathy) can predispose patients to entrapment neuropathies. Psoriasis has not been related to an increase in entrapment neuropathies.

Answer 31

B) Because the sensory nerve has no myoneural junction, the speed (V = D/T) can be directly calculated if the distance and the time (latency) is known. Motor nerves, on the other hand, have a myoneural junction. Since it is not known how long it takes for the action potential to cross the myoneural junction and for conduction in the muscle, the conduction velocity in a motor nerve must be calculated using the formula V = change in distance/change in time. Therefore, two stimulations must be performed (one proximal and one distal) to assess velocity. The difference in distance is divided by the difference in latency.

Answer 32

B) SSEPs may be helpful in diagnosing problems in sensory nerves such as in meralgia paresthetica, also known as lateral femoral cutaneous nerve injury) that are not accessible to routine electrodiagnostic testing. SSEPs are not the test of choice in assessing for a radiculopathy, as only the sensory pathway is tested and the pathway is very long. Problems anywhere along the pathway may affect latency and amplitude. They are not at all useful in assessing motor L nerves (anterior interosseous nerve injury). The pathway is too long to be of use in a sacral plexopathy.

Answer 33

C) Conduction block is a focal area of demyelination that is so severe that the action potential cannot propagate. Axonomesis is damage to the axon. Decreased amplitude will be noted if conduction block occurs between stimulator and recording electrodes (in both motor and sensory studies). If the conduction block occurs in the forearm, the distal amplitude will be normal, whereas conduction across the lesion will be affected. However, if the conduction block is distal, the distal CMAP and SNAP amplitudes would be affected (the lesion is in between the active electrode and the stimulator). This can easily be confused with an axonotmetic lesion. However, on needle testing, the axonotmetic lesion will show denervation or changes to the motor unit action potential (MUAP). Because conduction block is a focal problem with the myelin, no enervation should be noted on needle study.

Answer 34

A) 60-cycle (60-Hz) interference happens frequently and is usually caused by electrical sources near the MG machine. Turning on the notch filter will get rid of all components of the waveform that have 60-cycle components. Although this is usually a good thing (making the baseline flatter), the electromyographer must remember that just like all filters, you may be removing parts of the waveform that you want to see. Turning on the notch filter will remove part of the waveform, which may affect amplitude, latency, and conduction velocity as well as motor unit action potential (MUAP) morphology. Eliminating extraneous electrical currents and ensuring better electrical contacts may be a better solution.

Answer 35

A) Myotonic discharges wax and wane in frequency and amplitude. They may have an initial positive deflection and look like a positive sharp wave (PS), or they may appear as biphasic or triphasic potentials. They fire at variable rates (20-100 Hz) and sound like a "dive bomber." Myokymic discharges sound like marching soldiers. Myotonic discharges may be found in myotonic dystrophy, myotonia congenital, paramyotonia, hyperkalemic periodic paralysis, polymyositis, acid maltase defi ciency, and chronic radiculopathies and neuropathies.

Answer 36

D) Miniature end plate potentials are produced spontaneously by the release of one quantum of acetylcholine from the presynaptic terminal. End plate spikes are believed to be the result of single muscle fiber depolarizations. With needle EMG testing, there is usually increased pain when the needle is in the end plate region.

Answer 37

C) The motor point is the area where the nerve enters the muscle. This is usually located near the middle of the muscle belly. It is also known as the endplate zone.

Answer 38

B) It is very difficult to have the patient relax a muscle during needle testing. The best way to do this is to have the patient activate the antagonist muscle. This will automatically relax the muscle that you are testing. For example, if the needle is in the biceps muscle (which fl exes the elbow and supinates), have the patient extend the elbow and pronate. It is important to know the function of each muscle. As described above, simply extending the elbow will often not be enough to relax the biceps, since it also functions as a supinator.

Answer 39

B) When evaluating the recruitment pattern of MUAPs, it is important to use minimal recruitment. Ideally, you would like to see the fi ring rate of one motor unit when a second motor unit is recruited. If maximal recruitment is attempted, individual motor units cannot be assessed and the recruitment frequency cannot be assessed. In addition, there is a risk of the needle breaking in the muscle if the contraction is too strong.

Answer 40

B) The patient has the right to terminate the test at any point. It is best to explain the benefits of continuing the test and ask the patient whether they are sure that this is what they want. If the patient insists, this should be documented in the MG report.

Answer 41

A) Sensory amplitudes are generally about 10 to 20 microvolts. These are much smaller than motor (CMAP) amplitudes, where the gain is usually 1,000 microvolts. Remember that the gain is the Y-axis and is also called the "sensitivity." Therefore, a lower number (10 microvolts) represents a higher sensitivity than a higher number (1 millivolt). The waveform is the same. What differs is how much the waveform is "blown up" so that it can be visualized.

Answer 42

B) Since each "box" is 100 millivolts and since a CMAP amplitude is typically 5 to 10 millivolts in amplitude, the waveform would appear as a blip on the baseline. To adequately view the waveform, one would have to increase the gain by changing it from 100 millivolts to 1 millivolt.

Answer 43

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.

Answer 44

68. B) Hereditary neuropathies are usually uniform demyelinating neuropathies. They will therefore show uniformly slowed conduction velocity without temporal dispersion. Temporal dispersion would be seen in segmental demyelination, where some fibers are conducting much slower than others.

Answer 45

B) If the needle is in fat, atrophied tissue, periosteum, or subcutaneous tissue, the sound on the amplifier will not be crisp. If the needle is an adjacent muscle, the sound will be crisp with needle insertion (you are in a muscle). However, the rise time will be decreased when the muscle is activated, as you are not recording from the muscle that is being activated.

Answer 46

D) If the muscle that you are recording from is not innervated by the nerve you are stimulating, the recording electrode will pick up the electrical activity from a distant muscles that is being stimulated. However, this will result in an initial positive deflection. With a Martin-Gruber anastomosis, proximal stimulation of the median nerve will stimulate both the median nerve destined for the abductor pollicis brevis (APB) muscle and the ulnar nerve that is traveling with the median nerve (until the forearm where it crosses over). These ulnar nerve fibers innervate the nearby adductor pollicis muscle. Because the ulnar nerve does not have to traverse the carpal tunnel, the adductor pollicis muscle is stimulated before the abductor pollicis brevis (APB) muscle via the median nerve. Therefore, the recording electrode first picks up the distant action potential from the adductor pollicis, and a positive deflection is seen. This is especially evident when there is carpal tunnel syndrome and the median nerve is especially slow.

Answer 47

A) When many of the fibers that make up the CMAP have different velocities, the resulting waveform will be more dispersed. Remember that the latency reflects the fastest fibers. Those at the end of the CMAP reflect the slowest fibers. Even though this slowing is a result of a demyelinating lesion, the MAP amplitude may be decreased with temporal dispersion. Again, this is because there is a wider variation of conduction velocities and the CMAP has a longer duration. However, the area under the CMAP curve will be the same. Therefore, if a decreased amplitude is noted, do not automatically assume it is due to an axonal lesion. Assess the duration of the waveform. If it is prolonged, the decreased amplitude may be due to dispersion.

Answer 48

D) You cannot state that the patient has an St radiculopathy based solely on a prolonged H-reflex. Many conditions can lead to a prolonged H-reflex. To definitively state that the patient has a radiculopathy, there must be findings of enervation in the corresponding paraspinal muscle as well two limb muscles innervated by the same root level but different peripheral nerves.

Answer 49

D) Although the H-reflex is very sensitive, it is not specific. Any of the above conditions can result in a prolongation of the H-reflex.

Answer 50

C) Although this appears to be a simple right carpal tunnel syndrome, it is important (especially considering the enervation in the APB muscle) to rule out a median neuropathy more proximally, a double crush syndrome with cervical radiculopathy, or even an anterior horn cell disorder. Any of these can occur with a carpal tunnel syndrome. It is important to test a more proximal median innervated muscle (pronator teres) as well as another ulnarly innervated hand muscle. If these are positive, it behooves the electromyographer to continue the needle evaluation.

Answer 51

B) The axillary nerve comes off at the trunk level. With either an upper trunk or a lateral cord lesion, the musculocutaneous CMAP to the biceps, the lateral antebrachial SNAP, and the median SNAP will all be affected.

Answer 52

C) Orthodromic conduction means conduction in the same direction as physiologic conduction. For a sensory nerve, this would be an electrical impulse that is transmitted from the distal aspect of the sensory nerve (i.e., the finger or the toe) to the more proximal pickup. Sensory studies are usually performed antidromically (stimulating at the wrist or ankle and picking up more distally over the sensory area of the nerve).

Answer 53

B) Needle electrodiagnostic studies evaluate only large myelinated la fibers. This is the reason that in steroid myopathies (which usually affect type I fibers) the EMG will usually be negative.

Answer 54

C) The perineurium is a protective connective tissue that surrounds fascicles of myelinated and unmyelinated nerve fibers. The endoneurium is connective tissue that surrounds each individual axon and its myelin sheath. The epineurium is the loose connective tissue that surrounds the entire nerve.

Answer 55

B) Neurotmesis is complete transection of the nerve and involves the axon, the myelin, and all supporting tissue (connective tissue including the epineurium). There is complete disruption of any pathway, and nerve action potentials cannot propagate. There is little chance for regeneration (collateral sprouting or axonal regrowth) because of the loss of a pathway of connective tissue for the axon to follow. Neurapraxia is the same thing as conduction block. This is a focal area of severe demyelination. The demyelination is so severe that the action potential cannot propagate. As remyelination takes place, the myelin is immature. Therefore, with remyelination, there will be slowing of the segment where the conduction block occurred. Axonomesis is damage to the axon itself. However, the connective tissues and Schwann cells are intact, so recovery can take place.

Answer 56

A) The reference (G2) electrode is always placed distally over an electrically neutral area (i.e., tendon or bone). The EMG machine will "subtract" the electrical signal of the reference from the active electrode signal. Therefore, whenever possible, it is important that for motor studies, the reference be placed over an electrically neutral area.

Answer 57

D) Placing the surface reference electrode over the same muscle that the needle is in will decrease the baseline noise. The EMG machine will "subtract" the electrical signal of the reference from the active electrode signal. Therefore, any surface "noise" will be eliminated.

Answer 58

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.

Answer 59

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.

Answer 60

A) The motor units in a patient with steroid myopathy would typically have normal appearing motor units. That is because steroid myopathies typically affect type lI fibers. EMG testing evaluates type I fibers.

Answer 61

D) The Riche-Cannieu anastomosis is a communication between the deep branch of the ulnar nerve and the recurrent branch of the median nerve in the hand. It can produce an all ulnar hand. Therefore, if the ulnar nerve is injured proximally, the muscles normally innervated by the median nerve (but now innervated via the ulnar nerve anastomosis) may show signs of injury. Conversely, if the patient has a complete laceration of the median nerve at the wrist, he or she may still retain thenar function via the anastomosis.

Answer 62

A) The accessory peroneal nerve is a branch from the superficial peroneal nerve. It travels posterior to the lateral malleolus and innervates the lateral portion of the extensor digitorum brevis (EDB) muscle. The anomaly is usually noted when the amplitude of the compound motor action potential (CMAP) at the fibular head is larger than the MAP amplitude at the ankle. With stimulation behind the lateral malleolus, a CMAP is produced. Usually, the amplitude of the CMAP at the ankle combined with the amplitude of the CMAP posterior to the lateral malleolus equals the amplitude of the CMAP obtained at the fibular head.

Answer 63

A) The ground electrode should be between the recording and the stimulating electrodes. All of the other measures should help to decrease extraneous electrical noise.

Answer 64

C) The triceps and brachioradialis are innervated by the posterior cord via the radial nerve. The deltoid is innervated by the posterior cord via the axillary nerve. The biceps is innervated by the lateral cord via the musculocutaneous nerve.

Answer 65

B) The extensor carpi radialis is innervated by the radial nerve (C6/C7). The pronator teres is innervated by the median nerve (C6/C7). The flexor carpi radialis is innervated by the median nerve (C6/C7). However, the opponens pollicis is innervated by the median nerve (C8/T1).

Answer 66

B) The tibialis anterior is innervated by the peroneal (fibular) nerve (L4, L5, and some S1). The sartorius is innervated by the femoral nerve (L2, L3, L4). The adductor magnus is innervated by the obturator nerve (L2, L3, L4). However, the gluteus maximus is innervated by the inferior gluteal nerve (L5, S1, S2).

Answer 67

D). The saphenous nerve is the sensory continuation of the femoral nerve. It supplies sensation to the medial leg and foot.

Answer 68

D) The sural nerve receives sensory branches from both the tibial and the peroneal (fibular) nerves.

Answer 69

B) The short head of the biceps femoris is the only nerve that is innervated by the common peroneal (fi bular) nerve. It is also the only muscle innervated by the peroneal nerve that is above the popliteal fossa. Therefore, it is a very important muscle to test to determine the location of a lesion. The tibialis anterior muscle is innervated by the deep peroneal (fibular) nerve. The peroneus longus is innervated by the superficial peroneal (fibular) nerve, and the long head of the biceps femoris is innervated by the tibial nerve.

Answer 70

D) To assess whether a patient has a peripheral neuropathy, it is necessary to test sensory and motor nerves in three limbs. Therefore, the peroneal and sural (or any other sensory and motor nerve in the lower extremity) should be performed.

Answer 71

A) If the anode and cathode were reversed on the stimulator, there would be an extra 3 to 4 cm in length between the stimulator and the active electrode. The longer the distance that the stimulation has to travel, the longer the latency. If maximal stimulation were not used, the sensory and motor amplitudes may be decreased. If you did not stimulate over the nerve, the sensory and motor amplitudes may be decreased as well. If there was too much electrical interference, the baseline would not be fl at.

Answer 72

C) Diabetic neuropathy usually presents as sensory and motor, axonal and demyelinating peripheral polyneuropathy. Alcoholic neuropathy is usually a sensory motor axonal neuropathy. Paraneoplastic syndrome is usually a sensory axonal neuropathy. Guillain-Barré syndrome usually presents with segmental demyelination.

Answer 73

C) Insertional activity is a result of actual damage to the muscle membrane by the needle. It is normal if it lasts less than a few hundred milliseconds (just barely longer than the needle movement itself. The muscle should be at rest during this part of the testing.

Answer 74

C) The biceps is an elbow flexor, but it is also a strong supinator. To relax the biceps muscle, it is important to extend the elbow and pronate the forearm.

Answer 75

D) Dispersion is noted when the various components of the action potential travel at different speeds. Uneven degrees of demvelination and remvelination in the different nerve fibers make the entire MAP waveform of lower amplitude and longer duration. This is frequently seen in segmental demyelination. The area under the entire waveform is not decreased. The sum of all of the nerve fibers contributes to the shape of the CMAP. If some of the fibers are traveling at 30 m/sec, some at 40 m/sec, and some at 50 m/sec, the duration of the waveform will be prolonged (and the amplitude decreased. This can be confused with an axonal injury if the clinician only assesses amplitude, and not duration. In axonal injury, the amplitude is decreased, but the duration of the waveform is normal. Focal nerve slowing will present with a normal CMAP amplitude, but with conduction velocity slowing across the involved area. With conduction block, the CMAP amplitude distal to the lesion will be normal, but the CMAP amplitude will be decreased with stimulation across the lesion.

Answer 76

A) A more than 20% decrease in amplitude of the proximal segment (compared with the distal segment) usually indicates a conduction block. One must be careful to compare the affected with the nonaffected side. Sometimes if there is obesity or fluid accumulation proximally, the amplitude may be decreased because the stimulation is not close enough to the nerve. A 50% decrease in amplitude side to side usually indicates an axonal lesion.

Answer 77

D) The adductor magnus is innervated by both the obturator and the sciatic nerves. The superior gluteal nerve innervates the tensor fascia lata, the femoral nerve innervates the iliopsoas, and the obturator nerve innervates the gracilis.

Answer 78

C) The FDP is innervated by the median nerve (anterior interosseous branch) and the ulnar nerve. The median nerve innervates the FDP to digits 2 and 3, whereas the ulnar nerve innervates the FDP to digits 4 and 5. The pronator quadratus is innervated by the anterior interosseous nerve via the median nerve. The ulnar nerve innervates the flexor carpi ulnaris. The dorsal scapular nerve innervates the rhomboids.

Answer 79

D) The sartorius is innervated by the femoral nerve. The femoral nerve also innervates the pectineus, iliopsoas, and quadriceps muscles.

Answer 80

A) The accessory peroneal nerve is a branch of the superficial peroneal nerve that innervates the lateral aspect of the EDB. The nerve runs deep to the peroneus brevis and behind the lateral mallelus. The best way to test for this anomalous innervation is to stimulate the peroneal nerve posterior to the lateral malleolus (with pickup over the EDB). The amplitude of the CMAP obtained posterior to the malleolus plus (+) that of the normal ankle peroneal amplitude should summate and equal that of the amplitude proximally at the fibular head.

Answer 81

D) Froment's sign is a finding often found in ulnar neuropathy. It is demonstrated by having the patient grasp a piece of paper between the thumb and the radial side of the second digit. As the examiner tries to pull the paper out of the patient's hand, the patient will try to substitute his median innervated flexor pollicis longs muscle for a weakened ulnarly innervated adductor pollicis muscle.

Answer 82

C) Choice A describes myokymic discharges. It is often noted to sound like "soldiers marching" and is often seen in conditions such as multiple sclerosis, Bell's palsy, and polyradiculopathy. Choice B refers to neuromyotonic discharges. Generalized neuromvotonia is usuallv an autoimmune disease characterized by widespread muscle stiffness and delayed muscle relaxation after voluntary movement. Choice D refers to fibrillation potentials, which are usually triphasic in nature. Myotonia is clinically seen as delaved relaxation of a muscle after contraction. Potentials tend to fire at a variable rate, waxing and waning in appearance, and its variation causes a characteristic "dive bomber" sound."

Answer 83

A) Choice A describes axonotmesis, an injury to the axon that results in axonal S interruption with the connective tissue and Schwann cell remaining intact. Wallerian degeneration proceeds in a proximal to distal manner. Choice B refers to neuromesis, or nerve transection injury. This injury involves the axon and connective tissue disruption.' This leads to conduction failure. Choice C refers to neurapraxia, which is a nerve injury that results in focal myelin injury with an intact axon; conduction block is present.

Answer 84

D) The median nerve is known to have five classic areas of possible impingement. The ligament of Struthers (LOS) is a rudimentary ligament seen in only 1% of the population. It connects the medial epicondyle to a 2-cm bone spur that is a few centimeters proximal to the epicondyle. The median nerve, along with the brachial artery, can become entrapped under this ligament. The bicipital aponeurosis is a thickening of the antebrachial fascia, which attaches the biceps to the ulna and spreads over the median nerve in the forearm. The median nerve then travels between the two heads of the pronator teres muscle (where it can become entrapped and runs below the flexor digitorum superfi cialis. In pronator teres syndrome, the pronator teres muscle is usually not affected as the muscle receives its nerve innervation proximal to the nerve entering the two heads of the muscle. The anterior interosseous nerve, a motor branch of the median nerve, can be injured by a fracture of the forearm, compression, or laceration. Finally, the carpal tunnel syndrome is the most common site of median nerve compression.

Answer 85

D) The AIN is a motor nerve branch of the median nerve. An injury to this nerve results in a pure motor syndrome with no sensory deficits. The muscles innervated by the AIN are the flexor pollicis longus (FPL), pronator quadratus, and the flexor digitorum profundus (FDP) to digits 1 and 2. The FPL is usually the first muscle to be affected. As a result of the muscle impairments, patients are unable to approximate the thumb and index finger or give an "OK" sign.

Answer 86

D) The supraspinatus and infraspinatus are innervated by the suprascapular nerve, which originates from C5 and C6 roots. The trapezius is innervated by the spinal accessory nerve. Injury to this nerve can cause lateral winging of the scapula. The serratus anterior is innervated by the long thoracic nerve (C5, C6, and C7 roots), and injury to it can cause medial winging of the scapula. Remember SALT (serratus anterior long thoracic).

Answer 87

D) Diabetes (along with uremia) usually involves both the axon and the myelin with findings in motor and sensory fibers. Conditions associated with axonal motor polyneuropathy include porphyria and axonal L type Guillain-Barré syndrome. Hereditary neuropathies usually present with uniform demyelinating mixed sensorimotor polyneuropathy. Conditions that may present with segmental demyelinating motor polyneuropathy include Guillain-Barré syndrome (acute inflammatory demyelinating polyneuropathy) and hypothyroidism.

Answer 88

D) Alcohol abuse can lead to axonal injury to the nerves, involving both sensory and motor nerves. Thus, both CMAP and SNAP amplitudes would be expected to be decreased. Since the myelin is usually not affected, the conduction velocity and latency should not be affected.

Answer 89

D) The superficial peroneal nerve innervates the peroneus brevis and peroneus longs muscles. These muscles help to plantarflex and evert the foot. This nerve provides cutaneous sensation to the lower lateral aspect of the leg and dorsum of the foot with the exception of the first web space between the great and the second toes (innervated by the deep peroneal nerve). Choices A, B, and C are all innervated by the deep peroneal nerve along with the peroneus tertius and the extensor digitorum longus.

Answer 90

C) Radiculopathy is a lesion of a nerve root. Clinically, it may present as sensory, motor, or mixed sensory/motor findings. In radiculopathy, the injury is proximal to the area being stimulated and therefore conduction block or slowing of conduction velocity will not be noted on electrodiagnostic testing. Any damage to the sensory fibers is generally proximal to the dorsal root ganglion (DRG). Since there is physical continuity between the sensory nerve cell and the end unit, nerve conduction studies (NCS) will show normal sensory findings. Motor nerve conduction studies will generally be normal too because peripheral nerves contain multiple nerve roots. The classic needle EMG findings in a radiculopathy is abnormal spontaneous potentials (fibs and positive sharp waves) in the paraspinal muscles of the suspected root level as well as two muscles innervated by different peripheral nerves but the same root level.

Answer 91

C) Cooling results in longer time for the action potential to proceed down the axon. This is in part due to a change in protein configuration of the Na+ channels as its structure is changed by temperature change. Cooling can cause slow opening and even slower closing of Na+ channels, which slows the propagation of action potentials in axons. For every 1 °C drop in temperature, there is an approximate 5% decrease in conduction velocity. Amplitude is increased along with the duration of the action potential because of prolonged opening times of the sodium channels.

Answer 92

B) The serratus anterior is innervated by the long thoracic nerve (roots C5, C6, and C7), which helps to protract the scapula and rotate the glenoid upward. The supraspinatus is innervated by the suprascapular nerve (roots C5, C6), which helps in shoulder abduction and external rotation. The biceps brachii is innervated by the musculocutaneous nerve (roots C5, C6) and assists in elbow flexion and forearm supination. The rhomboids are innervated by the dorsal scapular nerve (solely C5 root) and help to elevate and retract the scapula as well as rotate the glenoid downward.

Answer 93

B) Although most radiculopathies are not clearly delineated by focal muscle weakness (since most are innervated by more than one root), this scenario clearly depicts a presentation consistent with a C6 radiculopathy. Wrist extensor weakness and brachioradialis weakness are consistent with a C6 level lesion. C5 radiculopathy would involve some weakness of the biceps, C7 weakness of the triceps, and C8 weakness of finger flexors.

Answer 94

D) The only muscle listed here that is not solely innervated by the obturator nerve is the adductor magnus. This muscle has dual innervation from both the obturator nerve and the tibial division of the sciatic nerve.

Answer 95

B) All the muscles listed above are dually innervated except for the gracilis. The flexor pollicis brevis is innervated by the median and ulnar nerves. The lumbricals are supplied by the median and ulnar nerves. The long head of the biceps femoris is innervated by the sciatic tibial division, whereas the short head of the biceps femoris is innervated by the common peroneal nerve. Only the gracilis is innervated by one nerve- the obturator nerve.

Answer 96

D) All the above statements about the H-reflex are true except for D. The H-reflex is a monosynaptic spinal reflex involving both motor and sensory fibers. Since it is a reflex and involves the la fibers, very little intensity is required (hence the submaximal stimulation, unlike the F-wave test). Increasing the intensity past the H-reflex peak amplitude will result in drop in H-reflex amplitude and an increase in M-wave amplitude. The H-reflex tests for the same fibers involved in the ankle reflex (S1) and can help in differentiating an L5 from an S1 radiculopathy. An H-reflex side-to-side difference of more than 1.5 milliseconds is considered significant.

Answer 97

D) All the above are valid limitations of the clinical utility of the H-reflEx. Since this reflex assesses a long neural pathway (including the orthodromic la afferents, the dorsal root ganglion to the spinal cord, interneurons, and then orthodromically to the muscle), a delay may not be specific to a radiculopathy. The lesion can be anywhere along the pathway.

Answer 98

C) F-waves are a delayed pure motor response. They are triggered by antidromic activation of motor neurons from peripheral stimulation of a nerve. This stimulation travels antidromically to the anterior horn cell; from there, it proceeds orthodromically to the muscle fiber. This backfiring ofthe axon is thought to represent a small portion (about 5%) of the orthodromically generated motor response (M-wave) that first occurs with stimulation. F-waves vary in their waveforms and latency and thus are averaged over multiple trials (usually 10). A-waves are seen in chronically injured nerves and represent regeneration or collateral sprouting of a nerve, as the orthodromic response is diverted along a collateral neural branch to circumvent the conventional path. This alternative path has a constant latency and is seen between the M- and the F-wave, with submaximal stimulation.

Answer 99

B) In repetitive nerve stimulation, a greater than 10% decrease in CMAP amplitude from the first to the fifth stimulation is considered significant for pathology at the neuromuscular junction.

Answer 100

D) In spinal stenosis, there is narrowing of the vertebral canal, which is usually exacerbated by extending the spine (standing) and relieved with flexion of the spine (sitting). Pain may radiate from the back down to the extremities, especially with extension of the spine. SNAPs are normal since the dorsal root ganglion (DRG) is located outside the spinal canal. CMAPs should not be affected as the distal portion of the nerve is not affected. There may be abnormal spontaneous potentials at rest (PSW or fibrillations) or chronic MUAP changes (polyphasic potentials) that are often bilateral. Bilateral paraspinals and extremities should be tested for EMG abnormalities.

Answer 101

C) A millivolt is one thousandth of a volt. A microvolt is a thousandth of a millivolt (or a millionth of a volt) this is a typical amplitude of a sensory nerve action potential (SNAP). The other choices are measures of time not amplitude. Amplitude is on the Y-axis, whereas time is on the X-axis of the EMG screen.

PMR 3 - EMG Flashcards

(125 cards)