Axonal multifocal motor neuropathy without conduction block or other features of demyelination

Conduction block is considered an essential finding for the distinction between motor neuropathies and lower motor neuron disorders. Only a small number of reports describe patients with multifocal motor neuropathies who lack overt conduction block, although in these cases other features of demyelination still suggest the presence of a demyelinating disorder. In contrast, a purely axonal multifocal motor neuropathy has not been described.

This report describes nine patients with slowly or nonprogressive multifocal motor neuropathies who had purely axonal electrodiagnostic features.

GM1 antibodies titers were normal in all nine cases. Six patients were treated with either prednisone or IV immunoglobulin and three showed convincing improvement.

These findings suggest an immune-mediated motor neuropathy with axonal electrophysiologic features that appears to be distinct from both multifocal motor neuropathy and established motor neuron disorders.