Natural history of 46 patients with multifocal motor neuropathy with conduction block

• Published in: Muscle & nerve Vol. 23; no. 6; pp. 900 - 908
• Main Authors: Taylor, Bruce V., Wright, R. Alan, Harper, C. Michel, Dyck, Peter J.
• Format: Journal Article
• Language: English
• Published: New York John Wiley & Sons, Inc 01-06-2000; Wiley
• Subjects: Action Potentials - physiology; Activities of Daily Living; Adult; Aged; Biological and medical sciences; Cranial nerves. Spinal roots. Peripheral nerves. Autonomic nervous system. Gustation. Olfaction; Electrodiagnosis; electrodiagnostic characteristics; Female; Follow-Up Studies; Humans; longitudinal changes; Longitudinal Studies; Male; Medical sciences; Middle Aged; Motor Neuron Disease - diagnosis; Motor Neuron Disease - physiopathology; Motor Neuron Disease - rehabilitation; Motor Neurons - physiology; multilocal motor neuropathy with conduction block (MMN-CB); Muscle Weakness - diagnosis; Muscle Weakness - physiopathology; Muscle Weakness - rehabilitation; natural history; Nervous system (semeiology, syndromes); Neural Conduction - physiology; Neurology; outcomes; Atrophy; Human; Nerve conduction; Evaluation; Nervous system diseases; Striated muscle disease; Pathogenesis; Multifocal demyelinating motor neuropathy; Upper limb; Diagnosis
• ISSN: 0148-639X; 1097-4598
• DOI: 10.1002/(SICI)1097-4598(200006)23:6<900::AID-MUS9>3.0.CO;2-Y

We studied 46 consecutive patients with multifocal motor neuropathy with conduction block (MMN‐CB). Typically, asymmetric weakness and atrophy of the hands or arms developed insidiously, but spontaneous improvement (without treatment) or death from this disease did not occur and 94% remained employed. For 18 patients examined on multiple occasions using the weakness subscore of the neuropathy impairment score [NIS(W)] for a median time of 2.3 years, worsening of 1.3 points per year was observed; many patients, however, had received intensive immunomodulating therapy. Median worsening to our first evaluation (generally without treatment) was estimated at 4.2 points per year, perhaps suggesting that treatment had influenced course. Three criteria for conduction block (CB) were compared, but the least stringent was sensitive for the diagnosis. Conduction block accompanied by weakness and atrophy typically affected only motor fibers, especially of midforearm nerves, and these sites of dysfunction persisted for months or years. Neurological signs and electrodiagnostic features were consistent with CB, axonal degeneration, a variable degree of reinnervation, and segmental demyelination. Although this study did not focus on therapy, intravenous gammaglobulin and cyclophosphamide appeared to be associated with neurological improvement, which was seldom complete or sustained. Axonal degeneration and faulty regeneration may in part explain this muted response. Possibly, treatment must be earlier, more intense, or different. © 2000 John Wiley & Sons, Inc. Muscle Nerve 23: 900–908, 2000