Minimal important differences and self-identifying treatment response in chronic inflammatory demyelinating polyneuropathy

Abstract

Introduction/aim: The use of outcome measures is recommended for chronic inflammatory demyelinating polyneuropathy (CIDP). Implications of minimal important differences (MID) to ascertain responder status are unknown. The reliability of patient-reported treatment-response in relation to clinically relevant change is also unknown.

Methods: We retrospectively studied 72 subjects with "definite" or "probable" CIDP evaluated at pre-specified time-intervals pre- and post-treatment. We derived MID and the minimum detectable change with 95% confidence intervals (MDC₉₅ ) for four scales. Scale sensitivities were determined with applicable MID-defined cutoffs (aMIDc), to detect subjects with self-identifying treatment response through a single question.

Results: The use of MID was not valid for the Medical Research Council Sum Score, as MDC₉₅ > MID. The aMIDc for the Overall Neuropathy Limitation Score (ONLS) was 1 (sensitivity: 84.7%). The aMIDc for the centile Inflammatory Rasch-built Overall Disability Scale (cI-RODS) was 8 (sensitivity: 62.3%). The aMIDc for grip strength was 4 kg (sensitivity: 79.1%). MID-defined amelioration of any one scale among ONLS, cI-RODS, or grip strength, significantly improved sensitivity to detect treatment-responders compared with the ONLS alone (McNemar test: P = .008, odds ratio: 3.36 [95% confidence interval: 1.44-7.86]). Patient-reported improvement was highly reliable in relation to MID-defined amelioration on any one scale.

Discussion: In subjects with CIDP, MID-defined amelioration of any one of three commonly used outcome measures offers optimum relevance and sensitivity to detect self-identifying treatment-responders. Patient reliability to single-question ascertainment of response is high in relation to MID-defined clinical relevance. These findings support use of multiple outcome measures in CIDP monitoring and justify enhanced patient involvement in the process.

Keywords: chronic inflammatory demyelinating polyneuropathy; minimum detectable change; minimum important difference; outcome measures; responders; self-identifying; sensitivity.