1. (C): The MUAP amplitude is slightly smaller than what is obtained with a monopolar needle. However the major spike rise time is shorter with a concentric needle than those obtained with a monopolar needle. The concentric needle does not require an additional reference electrode and is easier for patients to tolerate. However the thin Teflon-coated monopolar needles are better tolerated than the concentric needles. (Preston and Shapiro 1998, p. 146; Jun Kimura, p. 39)

2. (C): Insertion of a needle electrode into the muscle normally gives rise to brief bursts of electrical activity. The same discharges also occur with each repositioning. It appears as positive or negative high-frequency spikes in a cluster. Increased insertional activity may be seen in both neuropathic and myopathic conditions. In case of muscle being replaced by fat and fibrous tissue, insertional activity may actually be decreased. (Preston and Shapiro 1998, p. 182; Jun Kimura, p. 39)

3. (D): End-plate noise is low-amplitude, monophasic negative potentials that fire irregularly at 20 to 40 Hz and have a characteristic seashell sound on EMG. It represents extracellularly recorded miniature end-plate potentials (MEPPs), nonpropagating depolarization caused by spontaneous release of acetylcholine quanta. (Preston and Shapiro 1998, p. 183; Jun Kimura, p. 231)

4. (D): Fibrillation potential is derived from the extracellular recording of a single muscle fiber. These spontaneous depolarizations of muscle fibers are markers of denervation. They are typically associated with neurogenic disorders, may also be seen in muscle diseases and rarely in severe neuromuscular junctions disorders unless the condition is poorly controlled (especially in botulism). (Preston and Shapiro 1998, p. 184; Jun Kimura, p. 258)

5. (C): Fibrillations are brief spikes with initial positive deflection. They are of 1 to 5 ms in duration and low amplitude. Their firing pattern is very regular (0.5 to 10 Hz). The fibrillation potentials increase after warming the muscle or with administration of cholinesterase inhibitors. During cooling of the limb or with hypoxia the fibrillation discharges decrease. (Preston and Shapiro 1998, p. 184; Jun Kimura, p. 258)

6. (D): Positive waves are spontaneous depolarization of muscle fiber and signify denervation. They have positive polarity followed by a long negative phase. The absence of a negative spike implies recording near the damaged part of the muscle fiber. Positive waves are usually seen with fibrillation potentials but may be seen alone, sometimes early in denervation. The positive waves have variable amplitude but have a regular firing pattern. (Preston and Shapiro 1998, p. 184; Jun Kimura, p. 259)

7. (D): CRDs result from spontaneous depolarization of a group of muscle fibers firing in near synchrony. They result from the depolarization of a single muscle fiber followed by ephaptic spread to adjacent denervated fibers. The entire sequence repeats itself at slow or fast rates. The polyphasic and complex waveform remains uniform from one discharge to another. They have an abrupt onset and termination. CRDs less commonly are triggered by a stimulated MUAP or by a voluntary MUAP. (Preston and Shapiro 1998, p. 186; Jun Kimura, p. 262)

8. (C): A myotonic discharge is a spontaneous discharge of a muscle fiber and is characterized by its waxing and waning of amplitude and frequency. The firing rate is generally between 20 to 150 Hz. An individual myotonic potential may have a positive wave or brief spike morphology. Myotonic discharges are characteristically seen in myotonic dystrophy, myotonia congenita, and paramyotonia congenita. They may occur in some myopathies and in hyperkalemic periodic paralysis. (Preston and Shapiro 1998, p. 186; Jun Kimura, p. 253)

9. (B): A fasciculation is a single, spontaneous, involuntary discharge of an individual motor unit. It generally fires very slowly and irregularly between 0.1 to 10 Hz. The source generator is the motor neuron or its axon, proximal to its terminal. Fasciculations have the morphology varying from a simple MUAP to a complex and large if they represent a pathologic motor unit. Actual site of origin of most fasciculations has been found to be distal axon. They are brief twitches that seldom result in significant movement of a joint. (Preston and Shapiro 1998, p. 187)

10. (D): Distinguishing “benign” from “malignant” fasciculations on a clinical basis is nearly impossible. However, benign fasciculations are not associated with muscle weakness, wasting, or reflex changes. Benign fasciculations tend to fire faster and to affect the same site repetitively as opposed to malignant fasciculations that are more random. (Preston and Shapiro 1998, p. 29; Jun Kimura, p. G626)

11. (C): Myokymic discharges are rhythmic, grouped, spontaneous repetitive discharges of the same motor unit. The firing frequency within the burst is typically 5 to 60 Hz. The number of potential within a burst varies widely and may change from burst to burst. In between the bursts, the firing frequency is much slower. The myokymic discharges produce a marching sound on EMG. Changing to a longer not shorter sweep helps to recognize the myokymic discharge. (Preston and Shapiro 1998, p. 188; Jun Kimura, p. 259)

12. (B): Neuromyotonic discharges are bursts of motor unit action potentials, which originate in the motor axons firing at high rates for a few seconds and which often start and stop abruptly. The neuromyotonic discharges persist in sleep and typically have high frequency and a decrementing and waning pattern. EMG of cramps show full interference pattern of MUAP with normal morphology. This EMG pattern differentiates cramps from contractures. The EMG of contractures typically shows complete electrical silence. (Preston and Shapiro 1998, p. 189)

13. (B): In acute myopathies, the number of functioning muscle fibers in a motor unit decreases. This results in polyphasic shorter duration and smaller amplitude motor units. The other characteristic is early recruitment pattern. Polyphasic large motor units and delayed recruitment with rapid firing is a feature of neuropathic processes such as neuropathies, anterior horn cell diseases, and radiculopathies. In chronic myopathies, especially those with necrotic or inflammatory features, positive waves and fibrillations are commonly seen. (Preston and Shapiro 1998, p. 202)

14. (C): Early reinnervated motor units following severe denervation are known as nascent motor units. The key factor that differentiates nascent motor units from myopathic motor units is the recruitment pattern. Nascent MUAPs are always seen in the context of markedly reduced recruitment, whereas myopathic MUAPs are seen in the context of normal or early recruitment. (Preston and Shapiro 1998, p. 203)

15. (C): Tremor is recognized by a burst pattern of multiple MUAP firing simultaneously. The morphology of individual MUAP is difficult to assess as they tend to clump together. When tremor happens at rest, it can be mistaken for myokymia. In myokymia the same MUAP fires repetitively and continuously, whereas in tremor different MUAPs fire. In addition most patients can voluntarily alter their tremor by changing their limb position, whereas myokymia cannot be influenced by the patient. (Preston and Shapiro 1998, p. 205)

16. (D): The rate of axonal regrowth is limited by slow axonal transport. It is approximately 1 mm per day, so upper extremity axonal lesions will have a faster rate of recovery compared to lower extremities. It is much slower than the remyelination rate which only takes few weeks. Therefore, a demyelinating lesion with secondary axonal loss will have a more guarded prognosis than a purely demyelinating lesion. (Kimura, p. 68)