- 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 longus
C) Tibialis anterior, adductor magnus, biceps femoris
D) Tibialis anterior, gluteus maximus, peroneus longus
- 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
- 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
- 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 fi ndings
C) Peripheral neuropathy
D) Sensory carpal tunnel syndrome
- What is the difference in findings on electromyography (EMG)/nerve conduction studies (NCS) between someone with a conduction block and someone with an axonotmesis lesion distal to the point of stimulation?
A) The axonotmesis lesion will have decreased compound motor action potential (CMAP) amplitude, whereas the conduction block will not
B) They will have the same findings
C) Both will have decreased CMAP amplitudes, but only the axonotmesis lesion will have evidence of denervation on needle study
D) Both will have normal CMAP amplitudes, but only the sensory nerve action potential (SNAP) will be affected with an axonotmesis lesion
- The waveform below is most likely:
A) An end-plate potential
B) A fibrillation (fib) potential
C) A positive sharp wave
D) A motor unit
- Needle electrodiagnostic studies evaluate what types of fiber?
A) Only Ib (large, myelinated)
B) Only Ia (large, myelinated)
C) All A-alpha
D) Ia and Ib, myelinated
- To minimize electrical noise in the electro diagnostics (EMG) lab, you should do all of the following except:
A) Place the ground between the recording and the reference electrode
B) Make sure that the skin is cleaned appropriately (usually with alcohol)
C) Unplug equipment that is not being used
D) Turn off fluorescent lights
- In needle electromyographic (EMG) testing, insertional activity:
A) Is the result of discrete quanta of ACh
B) Is considered abnormal
C) Is the electrical activity generated as a result of disruption of the muscle membrane by a needle
D) Is performed with muscle activation
- Axonotmesis refers to:
A) An injury of the axon of a nerve but not the supporting connective tissue and results in Wallerian degeneration
B) Complete injury of a nerve involving the myelin, axon, and all supporting structures
C) A lesion where conduction block is present but the axon remains intact
D) A nerve injury that results in degeneration of the axon starting distally and ascending proximally
- A patient presents to your office with complaints of right arm weakness. On examination, you appreciate a positive Spurling’s test and notice mild weakness of the wrist extensors. With deep tendon refl ex (DTR) testing, you notice a diminished brachioradialis refl ex, but normal biceps and triceps DTR. At what root level do you suspect a radiculopathy?
- The combined sensory index (CSI) is used to assess:
A) Sensory axonal neuropathy
B) Sensory demyelinating neuropathy
C) Ulnar neuropathy at the elbow
D) Carpal tunnel syndrome (CTS)
- What is the most proximal muscle innervated by the common peroneal nerve?
A) Anterior tibialis
B) Short head of biceps femoris
D) Peroneus longus
- Why should the elbow be bent to about 90° 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
- When calculating a “normal” H-reflex, all of the following should be taken into consideration except:
D) Latency on the opposite side
- 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
- When performing a needle electromyographic (EMG) study, rise time of a motor unit action potential (MUAP) refers to:
A) Time for a motor unit to fi re
B) Time from baseline to initial negative peak
C) Time lag from the peak of the initial negative defl ection to the subsequent positive (down-ward) peak
D) Time from the baseline takeoff to when the waveform returns to baseline
- Somatosensory evoked potentials (SSEPs) may have utility in the diagnosis of:
B) Meralgia paresthetica
C) Anterior interosseous nerve injury
D) Sacral plexopathy
- What will happen if a compound motor action potential (CMAP) waveform is viewed at a gain of 100 mV?
A) It would appear truncated
B) It would appear as a small blip on the baseline
C) It would appear normal
D) It would appear half its size
- What would be considered orthodromic conduction for a sensory nerve?
A) Stimulating the wrist with a pickup over the fi nger
B) Stimulating the wrist with a pickup over the muscle
C) Stimulating the distal aspect of a fi nger and picking up more proximally over the wrist
D) Stimulating the distal aspect of a fi nger and picking up more proximally over the muscle
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- 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 superfi cial peroneal nerve.
- A) In an axonal injury, Wallerian degeneration occurs distal to the nerve lesion, and therefore, denervation 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.
- 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 (ie, how fast one motor unit is fi ring when another motor unit is recruited).
- 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 superfi cial (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).
- C) Conduction block is a focal area of demyelination that is so severe that the action potential cannot propagate. Axonotmesis 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 axonotmesis lesion. However, on needle testing, the axonotmesis lesion will show denervation or changes to the motor unit action potential (MUAP). Because conduction block is a focal problem with the myelin, no denervation should be noted on needle study.
- D) Although this waveform has an initial positive deflection, it is a motor unit. The gain is set at 1,000 mcV (ie, each box represents 1 mV). The waveform is much too large to be a fi b, a positive sharp wave (PSW), or an end-plate potential (which are usually seen when the gain is set at 100 mcV/division). If it were a fi b or PSW, it would appear as a very small blip on the baseline.
- B) Needle electrodiagnostic studies evaluate only large myelinated Ia fibers. This is the reason that in steroid myopathies (which usually affect type II fibers) the electromyography will usually be negative.
- 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.
- 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.
- A) Choice (A) describes axonotmesis, an injury to the axon that results in axonal interruption with the connective tissue and Schwann cell remaining intact. Wallerian degeneration proceeds in a proximal to distal manner. Choice (B) refers to neurotmesis, 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.
- B) Although most radiculopathies are not clearly delineated by focal muscle weakness (as 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.
- D) The CSI uses three parameters to increase the sensitivity for evaluating CTS using electrodiagnostic testing. Three parameters are tested: difference in the latency of the ulnar and median sensory response from digit 4 (at 14 cm), difference in the radial and median sensory response from the thumb (at 10 cm), and median and ulnar mid palm orthodromic stimulation (at 8 cm). If the added differences total more than 0.9 msec, CTS is confirmed.
- 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.
- 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. As speed = distance/unit of time, a falsely low distance will falsely slow the conduction velocity.
- C) H-reflex represents the time in milliseconds for a stimulation from the popliteal fossa to travel orthodromic in afferent sensory fibers, synapse in the spinal cord, and then travel orthodromic in efferent motor fibers to a pickup 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 msec 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.
- 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.
- 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 msec) 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.
- 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 nerves (anterior interosseous nerve injury). The pathway is too long to be of use in a sacral plexopathy.
- B) As each “box” is 100 mV and as a CMAP amplitude is typically 5 to 10 mV 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 mV to 1 mV.
- 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 (ie, 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).
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