Assessment Timing and Choice of Outcome Measure in Determining Treatment Response in Chronic Inflammatory Demyelinating Polyneuropathy: A Post-Hoc Analysis of the PRISM Trial

INTRODUCTION/AIMS: Treatment response and its timing are variable in chronic inflammatory demyelinating polyneuropathy (CIDP). We here aimed to study this variability with multiple outcome measures. METHODS: We performed a post-hoc analysis of the PRISM trial, a 24-week prospective, multicenter, single-arm, open-label, phase 3 study of a 10% intravenous immunoglobulin preparation for CIDP. We ascertained timing of response with primary/secondary outcome measures. RESULTS: At 6 weeks post-treatment initiation, 13/40 subjects (32.5%) were defined as responders on the primary outcome measure, the adjusted Inflammatory Neuropathy Cause and Treatment (INCAT) scale. This increased to 20/41 (48.8%) at 12 weeks and to 32/42 (76.2%) at 24 weeks. Use of minimal important difference (MID)-determined amelioration of the inflammatory Rasch-built Overall Disability Scale (I-RODS), or of the Medical Research Council Sum Score (MRCSS), or of dominant hand grip strength, in addition to the adjusted INCAT, offered a sensitivity of 41.7% in identifying adjusted INCAT non-responders at week 12 who subsequently responded at week 24. Specificity was 60% versus INCAT non-responders at week 24. Consideration of amelioration of any amplitude on any secondary outcome measure offered a 75% sensitivity but only 30% specificity versus adjusted INCAT non-responders at week 24. DISCUSSION: Immunoglobulin treatment continuation may be justified for up to 24 weeks in CIDP. Additional outcome measures may help in early treatment stages to predict delayed response on the adjusted INCAT. However, their use is limited by high false-positive rates. More robust, reliable and relevant outcome measures are needed to detect early improvement in immunoglobulin-treated CIDP. This article is protected by copyright. All rights reserved.