Multifocal motor neuropathy (MMN) is an acquired immune-mediated neuropathy characterized by chronic or stepwise progressive asymmetrical limb weakness without sensory deficits. The upper extremities are more often affected than the lower extremities with distal paresis dominating over proximal paresis. Important diagnostic features are persistent multifocal partial conduction blocks (CBs) and the presence of high-titer anti-GM1 serum antibodies. Motor neuron disease, other chronic dysimmune neuropathies, such as chronic inflammatory demyelinating polyneuropathy and the Lewis-Sumner syndrome (MADSAM neuropathy), are important differential diagnoses. While corticosteroids and plasma exchange are largely ineffective, high-dose intravenous immunoglobulins are regarded as first-line treatment. In spite of significant success in elucidating the underlying disease mechanisms in MMN during the past few years, important pathophysiological issues and the optimum long-term therapy remain to be clarified. The present review summarizes the clinical picture and current pathophysiological concepts of MMN with a special focus on the molecular and electrophysiological basis of CBs and highlights established therapies as well as possible novel treatment options.
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