[Multifocal motor neuropathy with persistent conduction blocks: 18 years on]

Area of Science:

• Neurology
• Peripheral Nervous System Disorders

Context:

• Multifocal motor neuropathy (MMN) is a rare peripheral nervous system disorder characterized by conduction blocks exclusively in motor nerves.
• First described in 1986, MMN presents as a progressive, asymmetrical neuropathy, primarily affecting the upper limbs of males over 50.

Purpose:

• To summarize the clinical presentation, diagnostic criteria, and current treatment landscape for multifocal motor neuropathy.
• To highlight the limitations of existing therapies in preventing long-term motor deterioration.

Summary:

• MMN is defined by motor nerve conduction blocks, with some patients exhibiting anti-GM1 IgM antibodies. Clinical features include multifocal, asymmetrical motor weakness, predominantly in upper limbs.
• Cerebrospinal fluid may show mildly elevated protein. Pathophysiology remains unclear, with the role of anti-GM1 antibodies debated.
• Intravenous immunoglobulin therapy provides short-term strength gains in 70-80% of patients but fails to halt progressive motor decline or new conduction blocks.

Impact:

• Current treatments like intravenous immunoglobulins offer symptomatic relief but do not address the underlying disease progression in multifocal motor neuropathy.
• Further research is needed to elucidate the pathophysiology of MMN and develop disease-modifying therapies.
• Corticosteroids and plasma exchange are ineffective, and the long-term efficacy of immunosuppressants is unknown.