The relationship between the quantitative assessment of the cross correlation between synkinetic pairs of muscles of the face in post Bell’s palsy synkinesis and the assessment of the spread of the R2 response from the orbicularis oris and a clinical assessment based upon the Sunnybrook score has been explored.
In the normal state the blink reflexes elicits a (late) R2 response limited to the orbicularis oculi muscles. However following significant facial palsy, and with the development of synkinesis the R2 response can be elicited in a more extensive distribution with activation of the orbital muscles around the mouth (orbicularis oris) and also to other muscles of facial expression including the platysma (Kimura Electrodiagnosis in Diseases of Nerve and Muscle). Although the R2 response from supra-orbital nerve stimulation is consistently seen in the orbicularis oris in patients with synkinesis, there was no relationship between the features of the R2 response and clinical assessment. This thus remains a method of documenting presence of synkinesis but cannot be used a surrogate marker.
Free running surface electromyography (EMG) is also very effective in the detection of synkinesis; during eye blinking bursts of EMG in muscles can be seen in muscles not usually associated with eye closure such as orbicularis oris and platysma in synkinetic muscle pairs. Co-contraction between synkinetic muscle pairs is also seen with sustained eye closure. The relationship of the surface EMG signal between pairs of synkinetic muscles can be quantified further by examining the degree of cross-correlation using signal processing techniques.
Evaluation of the magnitude of cross-correlation between the signals from synkinetic pairs of muscles may show a relationship with the degree of clinical synkinesis. Therefore further evaluation may be appropriate to see whether it is a quantifiable and objective metric of synkinesis severity.
(The analysis of previously collected data for clinical purposes has been reviewed and approved by the chairman of the local Newcastle ethical committee)