[Multifocal motor neuropathy with block of nerve conduction. Report of three cases]

Multifocal motor neuropathy is a severe chronic demyelinating, disimmune, crippling and potentially treatable disease. The clinical features are characterized by a syndrome of progressive motor deficiency with muscle atrophies, fasciculations, areflexia, myokimias and cramps, that sometimes we misdiagnosed as motor neuron disease. Electrophysiologically it is characterized by the occurrence of multifocal conduction blocks of motor fibres.

Three patients with asymmetric multifocal motor neuropathy are reported in whom diagnosis was made by nerve conduction studies. All the patients had developed an asymmetric chronic progressive motor deficit that involved mostly upper limbs. One patient exhibited mild tactile sensory disturbances and a sural nerve biopsy showed moderated involvement of myelinated fibers. All the patients showed electrophysiologically, multifocal conduction blocks of motor fibers with spared conduction through sensory fibers at the same segments where motor conduction was blocked. The response to high doses intravenous cyclophosphamide therapy followed by 100 mg orally for six months, was satisfactory in all three patients. There was no response to previous trials with prednisone, azathioprine, and intravenous immunoglobulin. One patient was also submitted to several sessions of plasma exchange without benefit. The patient had been previously diagnosed as having motor neuron disease.

The importance of early diagnosis of this disorder and the possibility of successful treatment with high doses of intravenous cyclophosphamide is stressed.