Electrophysiological Evaluation Practice Test

Pathological waveforms on EMG are signs of muscle fiber membrane instability and nerve-related disease. The key point is that these abnormal activities—positive sharp waves, fibrillations, fasciculations, complex repetitive discharges, and myotonic discharges—typically appear when the muscle is at rest. They arise because injured or denervated muscle fibers become irritable and fire spontaneously even without voluntary contraction. Positive sharp waves and fibrillations reflect single-fiber membrane instability, fasciculations are spontaneous motor unit activity, complex repetitive discharges are bursts seen in various neuropathic or myopathic states, and myotonic discharges occur with certain channelopathies and myotonic disorders. In contrast, a quiet EMG at rest would suggest no spontaneous pathology, and much of the rest of the activity seen with voluntary contraction relates to normal motor unit recruitment rather than spontaneous, irritative discharges.