The long-term effect of intravenous immunoglobulin treatment in multifocal motor neuropathy.

We studied the long-term effect of intravenous immunoglobulin (IV Ig) treatment in seven patients with multifocal motor neuropathy. In six patients, treatment with a full IV Ig course (0.4 g/kg for 5 consecutive days) improved muscle strength but for not longer than 12 weeks. These patients received IV Ig maintenance treatment consisting of one infusion every week for 2-4 years. One patient in whom the effect of the initial full IV Ig treatment lasted for more than 1 year received incidental IV Ig treatment when muscle strength deteriorated. In all patients IV Ig treatment had a beneficial effect on most muscle groups during the follow-up period. However, in three of the seven patients muscle strength deteriorated during IV Ig maintenance treatment in four of the 28 muscle groups that had initially shown an improvement of muscle strength after the start of IV Ig treatment, and in two muscle groups with normal strength at the start of IV Ig treatment. The electrophysiological follow-up studies indicated that there was an improvement of conduction block, but also that there were new sites of conduction block and ongoing axonal degeneration during IV Ig maintenance treatment.