Multifocal motor neuropathy mimicking motor neuron disease: nine cases

Multifocal motor neuropathy with persistent conduction block (MMN) is a rare clinical entity, mimicking motor neuron disease (MND). In order to research which are the most frequent nerves and segments where conduction block (CB) can be identified, we reviewed the clinical and neurophysiological data of nine patients with MMN who were studied and followed by the authors. Weakness and muscle atrophy of the dominant hand was the most frequent presentation. Lower limbs were involved later in the disease evolution. The ulnar and median nerves were the most affected nerves. They had conduction blocks mostly at the forearm and at Erb's point-elbow (or above elbow) segments. Both common peroneal and tibial nerves were frequently affected at their distal segments, but proximal segments were also probably involved. The presence of anti-GM1 antibodies was variable, and their determination was not essential for the diagnosis of MMN. Eight patients given IV immunoglobulin therapy had no disease progression. One patient was responsive to corticosteroids. The CB identification in our patients allowed us to clearly distinguish MMN from MND. The good prognosis and need for management with IV immunoglobulin, support the crucial role of a careful neurophysiological study to diagnose this clinical entity.