The value of MUNIX as an objective electrophysiological biomarker of disease progression in chronic inflammatory demyelinating polyneuropathy

Abstract

Introduction/Aims: Objective outcome measures to monitor treatment response and guide treatment are lacking in chronic inflammatory demyelinating polyneuropathy (CIDP). In this study we aimed to evaluate the motor unit number index (MUNIX) as an outcome measurement in patients with CIDP and determine the correlation of MUNIX with functional and standard electrodiagnostic tests in a single follow-up study. Methods: We evaluated MUNIX of the abductor pollicis brevis, abductor digiti minimi, and tibialis anterior (TA) muscles bilaterally. Muscle force was assessed by Medical Research Council Sum Score (MRCSS). Functional measures used were the Overall Neuropathy Limitation Score (ONLS) and the Rasch-built Overall Disability Scale (R-ODS) score at baseline and after 6 months of treatment. Standard electrophysiology was evaluated by the Nerve Conduction Study Score (NCSS). Results: Twenty patients were included at baseline, and 16 completed the follow-up study. Significant correlations were found between the MUNIX sum score and both MRCSS and NCSS at baseline, between both the pinch strength and grip and upper limb MUNIX at baseline and follow-up, and between MUNIX of TA and both lower limb MRCSSs with lower limb ONLS at baseline and follow-up. Significant correlations also were found between MUNIX sum score change and MRCSS change, R-ODS change, and ONLS change. Discussion: MUNIX changes correlated with strength and electrophysiological improvements in CIDP patients. This suggests that MUNIX may represent a useful objective biomarker for patient follow-up.