1. (C): F-wave is a pure motor response and represents a small CMAP representing 1% to 5% of the muscle fibers. Normal F-wave persistence is usually 80% to 100% but always >50%. F-wave can be obtained from any motor nerve. It is best obtained with distal stimulation. F-wave may be absent in sleeping or sedated patients and in some healthy patients particularly in the peroneal nerve. Supramaximal stimulation should be used with stimulator turned around so that the cathode is more proximal. One can record equally good F-waves without reversing the cathode and anode but the possibility of anodal block increases. (Preston and Shapiro 1998, p. 45)

2. (C): F-wave can be obtained from any motor nerve in lower extremity. It is best obtained with distal stimulation as proximal stimulation can result in superimposition of the F-waves on the terminal CMAP. Supramaximal stimulation must always be used and it is best to reverse the cathode and anode to eliminate the possibility of anodal block. F-wave latency is longer in tall patients. Mildly prolonged F-waves in tall patients should not interpreted as abnormal. (Preston and Shapiro 1998, p. 45)

3. (D): F-wave responses may have their greatest usefulness in identifying early polyradiculopathy such as occurs in GBS. GBS commonly begins with demyelination of the nerve roots before the distal nerve segments. Routine motor nerve studies may be normal in early GBS while F-wave prolongation may be the only sign of abnormality. Myasthenia gravis is a neuromuscular disease and F-wave response will not help to diagnose it. Diabetic sensory neuropathy will not affect the F-wave response because the F-wave is recorded solely from motor fibers. ALS may have prolonged or absent F-waves in later stage of the disease. However F-waves are rarely useful in establishing the diagnosis of ALS as the needle examination plays a much greater role. (Preston and Shapiro 1998, p. 50)

4. (C): H reflex is a true reflex with a sensory afferent (Ia sensory fibers) segment, a synapse, and a motor efferent segment. The typical H reflex latency is approximately 30 ms. Comparison with the contralateral side is more useful in assessing a unilateral lesion; any difference of >1.5 ms is considered significant. A supramaximal response will abolish the H reflex and commonly lead to the elicitation of an F-wave. Therefore, a slowly increasing submaximal stimulation is used to achieve H reflex. (Preston and Shapiro 1998, p. 54)

5. (C): Dislodging or movement of the recording electrode in relationship to the muscle movement may change the CMAP. RNS is obtained by supramaximal stimulation as a submaximal stimulation can create a CMAP decrement which can simulate a decrement and make the test false positive. Limb temperature can affect the test resulting in a false-negative study. CMAP decrement is diminished if the limb is cold. Pyridostigmine needs to be stopped 3 to 4 hours before the RNS as it makes more acetylcholine available to bind at the acetylcholine receptors and may potentially diminish CMAP decrements, resulting in a normal study or a decrement insufficient to establish a neuromuscular junction defect. (Preston and Shapiro 1998, p. 69)

6. (B): The optimal frequency for RNS is 2 or 3 Hz. This frequency is low enough to prevent calcium accumulation, but high enough to deplete the quanta in the immediately available store before the mobilization store starts to replenish it. For rapid RNS the optimal frequency is 30 to 50 Hz. (Preston and Shapiro 1998, p. 70)

7. (C): The lowest CMAP is usually the third or fourth stimulation. By the fifth or sixth stimulation the decrement begins to improve because the mobilization store of acetylcholine begins to resupply the immediately available store. Any decrement of >10% is defined as abnormal. Healthy subjects should have no decrement. (Preston and Shapiro 1998, p. 71)

8. (B): In patients with typical CTS, the median distal motor and sensory latencies and minimum F-wave latencies are moderately to markedly prolonged. However there is a group of patients with clinical symptoms and signs of CTS in whom these routine studies are normal (10% to 25%) In such patients the electrodiagnosis of CTS may be missed. (Preston and Shapiro 1998, p. 238)

9. (D): In comparison studies identical distances are used between the stimulator and recording electrodes for median and ulnar nerves. These techniques create an ideal internal control in which several variables that are known to affect conduction time are held constant, for example, distance, temperature, age, and nerve size. If the distal motor and sensory latencies are normal then comparison studies often are very helpful as they rely on patient’s own nerve rather than population normal values. (Preston and Shapiro 1998, p. 238)

10. (B): In normal individuals, the minimum F-wave latency from the median nerve is approximately 1 to 2 ms shorter than the minimum latency from the ulnar nerve. A reversal of that pattern is considered abnormal. The F-wave latency comparison is a nonspecific test because F-wave measures conduction along the entire length of nerve and cannot localize the lesion. Therefore it is used in conjunction with other sensitive tests. (Preston and Shapiro 1998, p. 245)

11. (C): Median F-wave latency assesses the whole length of the median nerve. However F-wave latency will be abnormal in both CTS and proximal median neuropathy. Similarly abductor policis will be affected in both conditions. Flexor carpi ulnaris is innervated by the ulnar nerve and will not be affected by any median neuropathy. Proximal median neuropathy at or proximal to the branch to pronator teres will result in acute denervation in the pronator teres muscle. (Preston and Shapiro 1998, p. 262)

12. (D): Ulnar motor studies in healthy subjects have shown a maximum drop in CMAP amplitude of 10% comparing below and above groove stimulation. Accordingly any drop in amplitude of >10% from below to above the groove is consistent with true conduction block. Minimal dispersion can be seen in healthy subjects and will not qualify for a conduction block. A drop in CMAP latency of 20% is significant but does not qualify as conduction block. (Preston and Shapiro 1998, p. 273)

13. (B): When stimulating at below-elbow site, the stimulator should be at least 3 to 4 cm distal to the groove (because the cubital tunnel length can be variable) to ensure a stimulation point distal to the cubital tunnel. The distance between below-elbow site to above-elbow site should not be <10 cm. If a short distance is used, slight errors in measurement may create large differences in calculated conduction velocities. Because the ulnar nerve is deep to the flexor carpi ulnaris at the below-elbow site, higher current is often required to ensure supramaximal stimulation of the ulnar nerve at this site. (Preston and Shapiro 1998, p. 276)

14. (D): If both ulnar motor and SNC studies are abnormal then it localizes the lesion at the elbow because the dorsal ulnar cutaneous sensory branch exits 5 to 8 cm proximal to the wrist to supply the dorsal medial hand. A lesion at the wrist will not affect the sensation in the medial hand. If all ulnar innervated muscles are abnormal and there is a conduction block at the elbow then it localizes the lesion at the elbow. If there is no conduction block then the ulnar neuropathy can be localized roughly, if the needle examination is abnormal to above the abnormal muscles. (Preston and Shapiro 1998, p. 277)

15. (A): C8-T1 radiculopathy will affect flexor carpi ulnaris and flexor digitorum profundus muscles which are ulnar innervated muscles and will not help in differentiating the two conditions. C8 fibers are also in the median nerve and will result in a low median CMAP amplitude. However, median CMAP amplitude will not be affected by ulnar neuropathy at the elbow. (Preston and Shapiro 1998, p. 271)

16. (B): In cases of radial neuropathy at the spiral groove, conduction block is seen with stimulation of the radial nerve proximal to the spiral groove. The relative drop in proximal to distal CMAP amplitude gives some indication of the proportion of fibers blocked. Most cases of posterior interosseous neuropathy are purely axonal in nature and a conduction block is usually not seen. A normal superficial radial sensory response is seen in posterior interosseous neuropathy because the superficial radial sensory nerve comes off before the posterior interosseous nerve. (Preston and Shapiro 1998, p. 291)

17. (D): Mononeuropathy multiplex is a distinctive pattern presenting as asymmetric, step-wise progression of individual peripheral and cranial nerves usually of the large nerves and not of small nerve twigs. As time passes, a confluent pattern may develop that is often difficult to distinguish from a diffuse polyneuropathy. Mononeuropathy multiplex is most commonly seen in the setting of vasculitic neuropathy. (Preston and Shapiro 1998, p. 273)

18. (C): Most patients with AIDP will have weakness as the predominant feature. As in most neuropathies affecting the axon, fibrillation potentials do not develop until 3 to 4 weeks after the onset of the illness. Early in the illness, the only EMG abnormality will be reduced recruitment of MUAPs that are normal in morphology. The prognosis of AIDP is worse in patients with low CMAPS, in those whose therapy with intravenous immunoglobulin (IVIG) or plasma exchange has been delayed >7 days, in patients with respiratory involvement, and in elderly patients. (Preston and Shapiro 1998, p. 362)

19. (D): CIDP on NCS typically shows markedly prolonged distal latencies (>130% of the upper limit), slow conduction velocity (<75% of the lower limit) and prolonged F-wave (>130% of the upper limit). It is a multifocal process and conduction block is seen. Secondary axonal involvement is the rule. Needle EMG shows evidence of chronic and ongoing axonal loss. Because CIDP is actually a polyradiculopathy rather than a polyneuropathy alone, changes are often also seen in the paraspinal muscles. (Preston and Shapiro 1998, p. 367)