Motor unit number index (MUNIX): Is it relevant in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP)?

•In CIDP, the MUNIX technique estimates the axonal loss and the number of functional motor units.•The MUNIX technique has a good intra and inter-rater reproducibility in CIDP.•The MUNIX sumscore is related to patients’ disability.

ObjectiveTo determine the test–retest reliability of motor unit number index (MUNIX) technique and to explore if the MUNIX sumscore could be related with disability in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP).MethodsThe MUNIX technique was unilaterally assessed in the abductor digiti mini (ADM), the abductor pollicis brevi (APB) and the tibialis anterior (TA) muscles two different times by two blinded examiners. The MUNIX sumscore was calculated by adding the results of the ADM, APB and TA muscles.Results14 CIDP patients were enrolled. The intraclass correlation coefficient (ICC) was great for inter and intra variability for ADM muscles (0.8 and 0.81), TA muscles (0.86 and 0.89) and MUNIX sumscore (0.76 and 0.83). The MUNIX sumscores from the first and second evaluations were strongly correlated (r = 0.83, p < 0.001). The MUNIX sumscore was significantly correlated with MRC testing (r = 0.71, p < 0.01), overall neuropathy limitation scale (ONLS) (r = −0.70, p < 0.001), rasch-built overall disability scale (R-ODS) (r = 0.71, p < 0.001).ConclusionsThe MUNIX technique has a good reproducibility and the MUNIX sumscore is related to the disability.SignificanceThe MUNIX technique estimates the axonal loss and the number of functional motor units. The MUNIX sumscore may be a good instrument to evaluate the CIDP patients during their follow-up.