Timing and Course of Clinical Response to Intravenous Immunoglobulin in Chronic Inflammatory Demyelinating Polyradiculoneuropathy

Objective: To investigate the timing, course, and clinical characteristics of the response to intravenous immunoglobulin in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Design: Data were extracted from the ICE trial, a randomized, double-blind, placebo-controlled trial of immune globulin intravenous, 10% caprylate/chromatography purified (IGIV-C). Setting: Multiple international centers. Participants: One hundred seventeen individuals with CIDP. Intervention: Treatment with IGIV-C (Gamunex, n=59) or placebo (n=58), with IGIV-C administered as a 2-g/kg loading dose followed by a 1-g/kg maintenance dose every 3 weeks, for up to 24 weeks. Main Outcome Measures: The primary efficacy parameter was an improvement of 1 or more points in adjusted Inflammatory Neuropathy Cause and Treatment (INCAT) disability score. Participants treated with IGIV-C were divided into subgroups based on meeting responder vs non-responder definitions and by time to first improvement. Results: Among 30 responders to IGIV-C, 14 (47%) patients had improved adjusted INCAT scores by week 3, and 16 (53%) patients improved at week 6 after a second infusion. Participants who improved by week 3 were more severely disabled at baseline than those who improved at 6 weeks. In patients who improved, the number of individuals reaching maximal improvement continued to increase during maintenance therapy for up to 24 weeks. For patients with first improvement by week 3, the change in dominant-hand grip strength over time tended to parallel the INCAT score. In patients with first improvement by week 6, however, the improvement in dominant-hand grip strength preceded initial improvement in INCAT score. Conclusions: Data suggest that treatment with 2 courses of IGIV-C administered 3 weeks apart may be required for initial improvement, and continued maintenance therapy may be necessary to achieve a maximal therapeutic response.