[Motor neuropathy with conduction blocks].

A series of 4 patients with pure, chronic and progressive motor neuropathy whose main clinical characteristics were asymmetric and distal weakness of the upper limbs, myokymia and fasciculations is presented. There were no sensory impairment and amyotrophy was observed in only one case. This picture suggested the diagnosis of motor neuron disease (MND). However, neurophysiologic examination demonstrated the presence of multifocal conduction blocks (CB) of the motor axons which were preferentially located in the proximal nerve segments and always at points atypical to nerve compression. The peripheral sensitive conductions and the somatosensory evoked potentials were normal, even through the nerve segments where the CB were located. Since this is a treatable potentially reversible syndrome, this motor neuropathy with CB should be included in the differential diagnosis of MND.