Continuous muscle fiber activity associated with denervation atrophy. Clinical presentation, electrophysiological and pharmacological investigations, histological and histochemical examinations of muscle biopsy.

We describe a case presenting continuous muscle fiber activity syndrome, which was slightly reduced by the blocking of nerve conduction and abolished by ischemia. Clinical, electromyographical and bioptical evidence of marked abnormalities of peripheral motoneurons were observed. Association with central motoneuron lesions was suspected due to the observation of initial pyramidal signs. Therapy with diphenylhydantoin and/or carbamazepine resulted only in discrete amelioration of the syndrome. This case, which presented similarities as well as differences to the cases described by Isaacs and to those reported by other authors after 1961, stimulates a critical discussion of the already raised problem of the clinical heterogeneity of continuous muscle fiber activity syndrome.