1. What is the clinical manifestation of conduction block?
B) There is no clinical manifestation
2. In myopathies, the motor unit action potentials (MUAPs) may demonstrate all of the following except:
A) Low amplitude
B) Long duration
D) Early recruitment
3. As opposed to acquired neuropathies, congenital neuropathies usually:
A) Have proximal more than distal slowing
B) Have uniform slowing throughout the nerve
C) Have segmental slowing throughout the nerve
D) Are distal
4. 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 (CMAPs)
B) Increased amplitude of sensory nerve action potentials (SNAPs)
C) Increased conduction velocity of SNAPs
D) Decreased amplitude of CMAPs
5. On needle electromyographic (EMG) 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
6. Miniature end-plate potentials are:
A) A postsynaptic response
B) A prerequisite for depolarization
C) The result of single muscle fiber depolarizations
D) The release of one quantum of acetylcholine from the presynaptic terminal
7. All of the following are possible reasons why a compound motor action potential (CMAP) would have an initial positive deflction except:
A) Not over the muscle you are trying to stimulate
B) Not stimulating the nerve that innervates that muscle
C) With proximal stimulation of the median nerve in a Martin-Gruber anastomosis
D) With distal stimulation of the median nerve in a Martin-Gruber anastomosis
8. While performing a motor nerve study, the reference electrode (G2) is placed:
A) Distally over an electrically neutral area (tendon or bone)
B) Proximally over an electrically neutral area (tendon or bone)
C) Distally over an electrically active area (muscle)
D) Proximally over an electrically active area (muscle)
9. All of the following muscles include innervation from the L4 nerve root except:
A) Tibialis anterior
B) Gluteus maximus
D) Adductor magnus
10. To diagnose a conduction block with electrodiagnostic testing, what percentage decrease in compound motor action potential amplitude should be noted from the proximal to the distal segment?
11. What muscle does the long thoracic nerve innervate?
D) Serratus anterior
12. Which of these statements regarding the H-reflex is not true?
A) This reflex is elicited with submaximal stimulation
B) As the intensity of the stimulation is subtly increased from the peak H-reflex amplitude, there is a gradual drop in H-reflex amplitude with a concomitant increase in M-wave amplitude
C) The H-reflex is often used to assess for S1 radiculopathy (with pickup over the gastrocnemius-soleus group), but can also be used to assess for C6/C7 radiculopathy with pickup over the flexor carpi radialis
D) Side-to-side differences in H-reflex latencies of greater than 1.0 msec are suggestive of S1 radiculopathies
13. In patients with myasthenia gravis, repetitive nerve stimulation will usually result in:
A) At least a 20% increment in amplitude between the first and fifth stimulation
B) No response
C) At least a 10% decrement in amplitude between the first and fifth stimulation
D) A decrease in the amplitude of the sensory response
14. Axonal damage (with Wallerian degeneration) 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
E) Slowing of conduction velocity distal to the lesion
15. In amyotrophic lateral sclerosis (ALS), the sensory nerve action potential (SNAP) will be:
B) Decreased amplitude distally and proximally
C) Decreased amplitude distally
16. 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
17. 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
18. If a patient has tarsal tunnel syndrome, one would likely fi nd 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
19. In needle electromyographic (EMG) testing, myotonic discharges:
A) May have an initial positive deflection
B) Are stable and do not change
C) Sound like marching soldiers
D) Are not seen in chronic radiculopathies
20. When the electromyographic (EMG) needle is inserted into the muscle, there is not a crisp sound and the feel of the needle is “gritty.” This may be a result of all of the following except: A) The needle has passed through the muscle and is touching periosteum
B) The needle is in an adjacent muscle
C) The needle is in fat
D) The muscle is atrophied
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- 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.)
- B) In myopathies, motor units usually have low amplitude (less than 1 mV when using a monopolar needle), short duration, polyphasicity, and early recruitment.
- 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.
- 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 latency is prolonged about 0.2 msec/°C, amplitude increases (sensory more than motor), conduction velocity decreases 1.8 to 2.4 m/s/°C, and duration increases. This is presumed to be due to sodium channels taking longer to open, but staying open longer, with cooling.
- 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 denervated 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.
- 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 fi ber depolarizations. With needle electromyographic (EMG) testing, there is usually increased pain when the needle is in the end-plate region.
- 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 muscle 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 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, median nerve is especially slow.
- A) The reference (G2) electrode is always placed distally over an electrically neutral area (ie, tendon or bone). The electromyography (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.
- 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).
- 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.
- 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).
- D) All the statements about the H-reflex are true except for choice (D). The H-reflex is a monosynaptic spinal reflex involving both motor and sensory fibers. As it is a reflex and involves the Ia 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 a 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 msec is considered significant.
- C) Myasthenia gravis is a disorder of the neuromuscular junction. Antibodies to the acetylcholine receptor affect the postsynaptic membrane. Repetitive nerve stimulation usually results in at least a 10% decrement in the amplitude between the first and fifth stimulation. Proximal muscles are affected more than distal muscles, so proximal muscles should be included in the testing. Sensory responses should be normal, as this disorder affects the neuromuscular junction. Testing should be performed with the muscle warm, and the patient should be off medication for myasthenia gravis. The test should be repeated after exercise of the muscle, and after 1-minute intervals to assess for postexercise exhaustion. Patients with myasthenia gravis have a 15% association with thymomas.
- A) Wallerian degeneration occurs distal to the level of an axonal injury. As with CMAP stimulation the pickup is always over a distal muscle, and both proximal and distal stimulation would result in decreased CMAP amplitude.
- 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.
- 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.
- 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%.
- 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.
- A) Myotonic discharges wax and wane in frequency and amplitude. They may have an initial positive deflection and look like a positive sharp wave (PSW), or they may appear as biphasic or triphasic potentials. They fi re 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 deficiency, and chronic radiculopathies and neuropathies.
- 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. ( Electrotherapy Quiz online )
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