New attempts to quantify concentric needle electromyography

Quantitative motor unit potential (MUP) analysis, which is a leading method of quantitative evaluation of concentric needle electromyography, has several inherent limitations. First, the most essential features of neurogenic or myogenic changes manifest as recruitment abnormalities, rather than as changes in MUP morphology. Second, two factors related to MUP sampling, focusing and level of contraction, greatly influence the parameters of sampled MUPs. Third, the MUP duration, considered to be the cardinal parameter in MUP analysis, has several drawbacks, including low stability and low discriminant sensitivity. We developed a new MUP parameter, the size index (SI), which is calculated from the MUP amplitude and area/amplitude ratio (thickness). The SI remained almost constant during electrode movements, as demonstrated by manual scanning of MUPs. It is a stable and robust parameter and achieved an extremely high ability to discriminate between normal and large neurogenic MUPs. It identifies features related to the sound produced by the MUP on the audio monitor, which is often used by trained electromyographers for qualitative assessments of MUPs.