Investigation of the Relationship between the Amplitude of the Maximum Responses of Compound Muscle Action Potential (CMAP) Scan and the Motor Unit Number Estimates (MUNE)

This study intends to exert the liaison between the Motor Unit Number Estimate (MUNE) and the Maximum Response of Compound Muscle Action Potentials (CMAPmax) of the CMAP Scan. MUNE is a neurophysiological method for diagnosing and monitoring Neuromuscular Disorders. CMAP Scan is a technique recording the responses of the gradually stimulated motor neurons. This process eventuates in a Stimulus-Response (SR) curve to monitor the courses of these disorders. Normal cases are demonstrated with a sigmoid curve in this plot. In case of Motor Unit (MU) loss requiring higher stimulus intensities the shape of SR curve gets changed. Therefore, the correlation MUNE with a feature less dependent to the shape of SR curve such as maximum CMAP might be investigated. Materials and Methods: Motor neuron (MN) groups with 5 to 300 axons were formed in a simulation software and they were stimulated by currents incrementally from 0 to 99 mA. The CMAPs which are the peak-to-peak voltage amplitudes (V
pp
) of the waveforms of CMAP traces are the responses to these currents in SR Curve. The maximum CMAP (CMAPmax) being the highest amplitudes of responses were found for each MN group. The coefficient of determination and the Pearson correlation coefficient between MU number and the maximum CMAP were found as 0.9976 and 0.999 respectively. This suggests a linear relationship between MU number and maximum CMAP. The maximum CMAP can be suggested as a new feature in building new mathematical models.