[Electrodiagnosis of neuromuscular diseases--a syndrome of monomelic amyotrophy with spinal hemiatrophy, anti-GM1 antibodies and abnormal F-waves (MASH)].

Electrodiagnosis rests upon sound anatomical and physiological bases of the peripheral nervous system, which are utilized for the dynamic process of differential diagnosis. If clinical and electrophysiological findings do not conform to any of the previously known diseases, there may be a chance of identifying a new entity. As an example, we report nine Japanese patients with unilateral atrophy of the distal upper limb and the cervical cord. Symptoms typically began insideously in young adulthood, progressed for a few years and then stabilized. Distribution of the muscle weakness usually corresponded to the territories of a few peripheral nerves, although not accompanied by sensory deficits. Serum anti-GM1 IgG antibodies were elevated in 6 out of 9 patients. Electrophysiological testings disclosed absent or delayed F-waves in the nerve involved. No long tract signs of the cord were demonstrated, although the spinal cord atrophy was extensive in some patients. Three showed partial clinical improvement after cyclophosphamide therapy or intravenous immunoglobulin. These findings may suggest that this entity is immune-mediated as in multifocal motor neuropathy, with its blunt of immune attack directed not only to peripheral motor nerves but also to spinal motor neurons.