Multifocal Motor Neuropathy with Conduction Block: Current Issues in Diagnosis and Treatment

Multifocal motor neuropathy (MMN) with conduction block is an acquired, autoimmune-mediated neuropathy that is responsive to treatment. The clinical history is one of slowly, progressive distal weakness, which more commonly involves the upper extremities, and it affects mainly young adults. Physical examination reveals weakness without sensory loss in the distribution of individual nerves. Atrophy may be present, but hyperreflexia and spasticity are not seen. Electrophysiological studies reveal motor conduction blocks at sites not prone to compression with normal sensory responses. Immunoglobulin M anti-GM1 titers may be elevated. Treatment with human immunoglobulin or cyclophosphamide has been shown to improve strength in the majority of patients with MMN in the short term. However, motor strength and function may gradually decline over years in spite of long-term therapy.