Therapeutic plasma exchange in multifocal motor neuropathy

Background: Although there is evidence for an important role of an aberrant humoral immune response in the pathogenesis of multifocal motor neuropathy (MMN), plasma exchange (PE) has been considered to be an ineffective treatment. The reason for this contradiction is unknown and available data about the use of PE in MMN is sparse. Therefore we retrospectively analyzed the clinical efficacy of therapeutic PE and determined reasons for treatment failure of PE in patients with MMN.

Methods: Clinical characteristics, electrophysiological parameters, and anti-ganglioside antibody titers in seven patients with MMN, who underwent four to six cycles of PE, were retrospectively reviewed.

Results: Only two out of seven patients exhibited a transient clinical response to PE, manifested by improved neurological function. Whereas electrophysiological parameters continued to worsen in all patients, anti-ganglioside antibody titers declined during PE, but increased after this therapeutic intervention.

Conclusion: PE is of limited therapeutic value in MMN and may only be useful as an adjunctive treatment in a subset of patients. The transient decrease of anti-ganglioside-antibodies titers suggest that potentially pathogenic humoral factors in MMN are only temporarily reduced. Moreover, PE treatment alone is insufficient to prevent axons from ongoing degeneration, which may explain the failure of PE to substantially modulate the disease course in patients with MMN.