Utility of the Clustering Index method for diagnosing neuromuscular disorders as compared with needle electromyography.

Introduction/aims: Concentric needle electromyography (CNEMG) is an essential examination for evaluating neuromuscular disorders, although pain is a drawback. Clustering Index (CI) method is a non-invasive quantitative analysis for surface electromyography (SEMG) that evaluates whether the signal area is clustered into the few large motor unit potentials (MUPs) or is evenly distributed. However, the diagnostic yield of the CI method in comparison with CNEMG is not known. In this study, we aimed to compare the sensitivity of the CI method with MUP parameters in CNEMG for diagnosing neurogenic or myogenic disorders.

Methods: We retrospectively identified patients for whom both SEMG and CNEMG were performed on the same tibialis anterior (TA) muscle. In CNEMG, seven MUP parameters were evaluated, including size index (SI) and revised size indices for neurogenic (rSIn) and myogenic (rSIm) disorders.

Results: Identified were 21 patients with neurogenic and 21 patients with myogenic disorders. Control data were constructed from 30 control subjects. The sensitivities of the CI method for the neurogenic and myogenic groups were 76% and 62%, respectively, which were not significantly different from MUP parameters, except for being significantly higher than those of amplitude and duration for myopathy (24%). Among MUP parameters, the sensitivities of rSIn (62%) and rSIm (57%) for myopathy were significantly higher than those of amplitude and duration. The CI method significantly correlated with the strength of the TA muscle in myopathy.

Discussion: The CI method, having comparable diagnostic yields to MUP parameters, is promising as a non-invasive diagnostic measure.