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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.

Summary Morphological features of the central nervous system, by light and electron microscopy, are reported in various encephalopathies by inborn enzymatic defect in lipid, glucidic and aminoacid metabolisms. The authors stress on the caracteristics of the abnormal storage material in Neurolipidoses, Ceroid-Lipofuscinoses, Glycogenosis type II and Lafora disease. On the other hand, they insist on the non specific lesions of the central nervous system in Aminoacidopathies by enzymatic defect.

Summary A predominance and/or an atrophy of type I fibers and a loss of deep tendon reflexes are often observed in different types of congenital myopathy. Various data indicate that both findings can be linked: dysfunction of the myotatic reflex can induce predominant involvement of type I fibers. In order to specify the mechanism of the loss of tendon reflex, an investigation of the Hoffmann reflex (H reflex) was performed in one case of centronuclear myopathy and in one case of congenital type fiber disproportion with type I hypertrophy. The Achilles tendon reflex was absent but the H reflex showed normal recruitment amplitude and latency. The Jendrassik maneuver reinforced the H reflex. These results indicate the involvement of muscle spindles or impairment of the fusimotor system. Nuclear bag intrafusal fibers have common characteristics with type I extrafusal fibers. Both types of fibers could be involved simultaneously in congenital myopathles, thus explaining the loss of tendon reflex.