Slow resolution of multifocal weakness and fasciculation: a reversible motor neuron syndrome.

A 25-year-old man with multifocal weakness and fasciculation was thought to have motor neuron disease. Signs progressed for 1 year, plateaued, and 3 years later resolved almost completely. There was no evidence of paraproteinemia, lymphoproliferative disorder, or vasculitis, and myelography was normal. Electrodiagnostic study disclosed multifocal, acute and chronic denervation that evolved into a picture consistent with residuals of old multifocal radiculopathy without active denervation. Prolongation of F response, absence of H-reflex, and conduction block in a proximal nerve segment suggested multifocal demyelination. A proximal motor neuropathy, perhaps demyelinating, may cause some of the benign motor neuron syndromes that simulate motor neuron disease.