Motor unit number index correlates with disability in Charcot-Marie-Tooth disease

Abstract Objective The aim of this study was to assess the usefulness of motor unit number index (MUNIX) technique in Charcot-Marie-Tooth disease and test the correlation between MUNIX and clinical impairment. Methods MUNIX technique was performed in the abductor pollicis brevis (APB), the abductor digiti minimi (ADM) and the tibialis anterior (TA) muscles in the nondominant side. A MUNIX sum score was calculated by adding the MUNIX of these 3 muscles. Muscle strength was measured using the MRC (medical research council) scale. Disability was evaluated using several functional scales, including CMT neuropathy score version 2 (CMTNSv2) and overall neuropathy limitation scale (ONLS). Results A total of 56 CMT patients were enrolled. The MUNIX scores of the ADM, APB and TA muscles correlated with the MRC score of the corresponding muscle (p  r   =  −0.65, p  r   =  −0.57, p  Conclusion MUNIX correlates with muscle strength and clinical measurements of disability in patients with CMT disease. Significance The MUNIX technique evaluates motor axonal loss and correlates with disability. The MUNIX sum score may be a useful outcome measure of disease progression in CMT.