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

We studied 46 consecutive patients with multifocal motor neuropathy with co nduction block (MMN-CB). Typically, asymmetric weakness and atrophy of the hands or arms developed insidiously, but spontaneous improvement (without t reatment) or death from this disease did not occur and 94% remained employe d. For 18 patients examined on multiple occasions using the weakness subsco re of the neuropathy impairment score [NIS(W)] for a median time of 2.3 yea rs, worsening of 1.3 points per year was observed; many patients, however, had received intensive immunomodulating therapy. Median worsening to our fi rst evaluation (generally without treatment) was estimated at 4.2 points pe r year, perhaps suggesting that treatment had influenced course. Three crit eria for conduction block (CB) were compared, but the least stringent was s ensitive for the diagnosis. Conduction block accompanied by weakness and at rophy typically affected only motor fibers, especially of midforearm nerves , and these sites of dysfunction persisted for months or years. Neurologica l signs and electrodiagnostic features were consistent with CB, axonal dege neration, 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 rege neration may in part explain this muted response. Possibly, treatment must be earlier, more intense, or different. (C) 2000 John Wiley & Sons, inc.