[Electromyographic aspects of inclusion body myositis. Macro-electromyographic study]

Histological and electrophysiological features in cases of inclusion body myositis are often difficult to interpret, suggesting either a "myogenic" or a "neurogenic" disorder. One case of inclusion body myositis is described. Conventional needle electromyography recording was interpreted as "neurogenic": abundant fibrillation potentials and positive sharp waves, reduced interference pattern, polyphasic-high amplitude-long duration motor unit potentials. Macro-EMG was performed in quadriceps muscle. Fibre density was normal and median value of the amplitude of macro motor unit potentials was increased, suggesting a larger size of motor units. Morphologic and electrophysiologic features indicate compensatory and regeneration mechanisms resulting in an increase of motor unit during the course of inclusion body myositis. This can explain atypical electromyographic and morphologic data in this disease.