3-2-12. Size index revisited: Verification by increased number of subjects

Abstract

Size Index (SI) is a motor unit potential (MUP) parameter in concentric needle EMG, which can sensitively discriminate between control and neurogenic MUPs. We also proposed the revised SI (rSI) using a logarithmic scale for area/amp. In this study, we greatly increased the number of patients, and investigated the utility of SI and rSI for both neurogenic and myogenic MUPs. The biceps brachii (BB) and tibialis anterior (TA) muscles were investigated. The study population was 1619 control MUPs (26 subjects), 340 neurogenic MUPs (10 subjects), and 498 myogenic MUPs (14 subjects) in BB, and 1245 control MUPs (23 subjects), 566 neurogenic MUPs (19 subjects), and 473 myogenic MUPs (13 subjects) in TA. The coefficient for area/amp was variously changed for SI and rSI. As results, the maximum sensitivity of SI for neurogenic MUPs was 84% for BB and 66% for TA. Similar sensitivity was achieved using rSI. That for rSI for myogenic MUPs was 9% for BB and 25% for TA. These were higher than any other conventional parameters. By choosing appropriate coefficients, SI (for neurogenic MUPs) and rSI (for both neurogenic and myogenic MUPs) will enhance the utility of MUP analyses.