How long is IVIg effective in multifocal motor neuropathy?

The authors treated 10 patients with multifocal motor neuropathy (MMN) responding to an initial course of IV immunoglobulin (IVIg) with periodic infusion for 5 to 12 years (mean 8.2 years). At last follow-up, only two patients had maintained the maximal improvement achieved during therapy while eight worsened despite increasing Ig dosage. This decline started after 3 to 7 years (mean 4.8 years) of therapy and correlated with a reduction of distal compound muscle action potential amplitudes (p < 0.019). The effectiveness of IVIg in MMN often declines after several years possibly associated with the development of axonal degeneration.