Objective: The aim of the study was to determine whether 'clouds' from turns amplitude analysis obtained from the orbicularis oculi and oris muscles without force monitoring can be used to differentiate pathological processes affecting the face.
Methods: The interference pattern from orbicularis oculi and orbicularis oris was studied using a concentric needle electrode. Data-points from 20 normal subjects were plotted on a logarithmic scale of mean amplitude between turns versus turns/second, from which linear regression analysis defined the 95% confidence intervals. This enabled us to draw the boundaries of the normal cloud on a linear plot. Data-points from the interference pattern in two pathological cohorts, of 6 patients receiving botulinum toxin injections (representing a neurogenic model), and 6 patients with a muscle dystrophy (representing a myopathic model) were plotted against the normal cloud. These findings were compared and correlated with the mean durations obtained on motor unit action potential analysis from these same two facial muscles.
Results: The majority of patients receiving botulinum toxin injections into their facial muscles showed a pattern of high amplitude with low turns/s, or low amplitude with a low-to-normal range of turns/s in both facial muscles. These findings were associated with high-duration motor unit action potentials in most cases. In the myopathic group of patients 66% showed a pattern of low amplitude with low-to-normal range of turns/s in O oculi and O oris. This correlated with short-duration motor unit action potentials in both facial muscles.
Conclusions: We have demonstrated that turns amplitude analysis without force monitoring can be used to study the interference pattern from facial muscles and can be applied to differentiate primary neurogenic from myopathic pathological processes.
Significance: Turns amplitude analysis without force monitoring in the facial muscles can be used as an effective and practical method of interference pattern analysis to complement findings from conventional motor unit action potential analysis.