Synchronous surface electromyography as objective method to evaluate the outcome of a biofeedback training in patients with facial synkinesis

Facial aberrant reinnervation after unilateral facial paralysis is characterized by facial synkinesis and global facial muscle hypertonicity. Therefore, therapy effort is directed on improved facial symmetry by reducing facial synkinesis and the elevated muscle tone. There are no established methods to confirm these aims objectively. Therefore the aim of the present study was to verify if high-resolution surface electromyography (HR-sEMG) mapping of the entire face during standardized facial movements is one such sought-after method. Bilateral HR-sEMG facial mapping was performed in 36 patients (81% women; age range: 24-70 years) with a postparalytic facial nerve syndrome. Participants performed a standard set of standardized facial movement tasks before start (T0) and after nine days of training (T9). A linear mixed-effects model was used to evaluate differences between the facial movement tasks in-between the synkinetic side and the contralateral side at T0 and T9. The overall facial muscle activity was higher on the synkinetic side compared to the contralateral side at T0 (p < 0.001) and also at T9, but with reduced difference between sides (p ≤ 0.002). The overall muscle activity decreased on the synkinetic side and on the contralateral side (both p < 0.001). These effects were also verifiable for almost every investigated muscle. HR-sEMG facial mapping proved its suitability as an objective method to confirm facial feedback training effects: A combined visual and EMG-based facial biofeedback training seemed to reduce the facial muscle activity on both facial sides, but markedly more effective on the synkinetic side.