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

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. Objectives: To confirm if MUNIX reflects motor unit loss and clinical stage and to assess difference in MUNIX and EMG results between muscles in different stage. Methods: 132 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). Results: In 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. Conclusions: MUNIX reflects motor dysfunction and could be a good biomarker for loss of motor neurons in PPS.