Non-invasive quantitative EMG: invention of the "Clustering Index (CI)" method]

There have been few previous studies trying to evaluate neuromuscular disorders using surface electro myography (SEMG). The greatest obstacle to such an approach must be the difficulty in identifying individual motor unit potentials (MUPs) on the SEMG signal under voluntary contraction because of their dense overlap. We tried to solve this problem by reducing the overlap of MUPs using appropriate electrode setting, as well as by developing a new method of interference pattern analysis. The tibialis anterior muscle was examined in our first study. A new method to analyse SEMG signal, the Clustering Index (CI) method, achieved 100% and 61% sensitivities for neurogenic and myopathic patients, and 97% specificity for control subjects. In the second study, the abductor digiti minimi muscle was examined. Subjects were 29 spinal and bulbar muscular atrophy patients and 27 controls. The CI method was compared with the motor unit number estimation, and the amplitude of compound muscle action potential. As results, the CI method achieved the best sensitivity and among these three techniques. The CI method is a novel, simple, and quantitative analysis method without using any special equipments, and is promising as a non-invasive complement to needle EMG.