Motor Unit Number Index (MUNIX) as a biomarker of motor unit loss in post-polio syndrome versus needle EMG

Abstract

MUNIX method (Motor Unit Number Index) had been not used to assess number of motor neurons in post-polio syndrome in contrary to needle electromyography. ObjectivesTo confirm if MUNIX reflects motor unit loss and clinical stage and to assess difference in MUNIX and EMG results between muscles in different stage. Methods132 Muscles (MUNIX) and 96 (EMG) in 12 patients were studied and divided into groups: with normal strength(N), stable weakness and atrophy(S), new weakness and atrophy(W). ResultsIn PPS group MUNIX global was 561.36 ± 282.6 (right 6 muscles) and 561.27 ± 281.1 (left) significantly lower than in control group (six muscles 1139.6 ± 164.5) (p < 0.05). MUNIX global correlated with MRC global. MUNIX was greater in muscles with normal strength (95–100% of normal values) than in those with stable weakness (48%-0% of normal values) and new weakness (65%-0% of normal values). Respectively to clinical stage of muscle MUP (motor unit potential) amplitude increased to 350% of normal value, from 250% to 110%, and from 300% to 700%. No correlation was found between MUP parameters and MRC values. ConclusionsMUNIX reflects motor dysfunction and could be a good biomarker for loss of motor neurons in PPS.