Quantitative electromyography of the frontalis muscle

Abstract

Purpose: Identification of abnormal motor unit potentials (MUP), in particular those caused by myopathic processes, is generally difficult in facial muscles because the MUPs are already low in amplitude and short in duration. Therefore, quantitative measures for the limits of abnormality are needed more frequently for these muscles, especially for the pathological processes predominantly affecting the craniofacial area. In this study, we aimed to determine some quantitative values that may help us to differentiate "myogenic" and "neurogenic" processes in periocular muscles.

Methods: The frontalis muscle was examined unilaterally with multi-MUP and interference pattern analyses in 32 normal subjects, 31 patients with different types of myopathy, and 13 patients with facial palsy. Abnormality limits were calculated by using five previously suggested methods, two of which were based on group means and the other three on determining the outlier values. The sensitivity and specificity of multi-MUP and interference pattern parameters in discriminating abnormal findings by using these different methods were analyzed.

Results: Statistically significant differences for all MUP parameters, except for the frequency, was found between the groups (P < 0.001). Motor unit potential duration, size index, and amplitude were the most valuable parameters for distinguishing the individual abnormalities. However, their discriminating power was higher for neuropathies than for myopathies. Interference pattern analysis was found not to have any superior sensitivity to MUP analysis. In this study, the outlier analysis that depends on the 5th to 95th percentile limits of the pooled data provided the best power for the discrimination of both neuropathies and myopathies from normal subjects.

Conclusion: Multi-MUP analysis seems to be helpful in differentiating the patients with neurogenic and-to a lesser extent-myogenic facial muscle involvement.