Which clinical history findings are characteristic of multifocal motor neuropathy (MMN) with conduction block?

Updated: Nov 12, 2018
  • Author: Sasa Zivkovic, MD, PhD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Typically, multifocal motor neuropathy (MMN) manifests with a slowly progressive, asymmetric, predominantly distal weakness developing over years. Weakness usually starts in a distribution of a single peripheral nerve with unilateral wrist drop, foot drop, or grip weakness. Initial involvement of the distal upper extremities is most common. Rarely, MMN may manifest with initial phrenic or cranial nerve involvement. Cramps and twitching are common, but muscle atrophy is minimal if present at all. Sensory symptoms are minimal or absent. Transient exacerbation may occur during pregnancy. As with other neuromuscular disorders, patients also commonly complain of fatigue.

Electrodiagnostic evaluation may document the presence of asymptomatic conduction blocks in other clinically unaffected nerves, and it may document more extensive involvement in patients with relatively few symptoms. Positive serology for anti-GM1 antibodies is supportive of the diagnosis of MMN, particularly higher titers.

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