Clinical Perspectives on the Pathophysiology of Facial Synkinesis: A Narrative Review

Facial synkinesis refers to pathologic cocontraction and baseline hypertonicity of muscles innervated by the facial nerve, commonly attributed to the aberrant regeneration of nerve fibers following injury. The pathomechanism and optimal treatment of facial synkinesis remain unclear. The goal of this review is to highlight current understanding of the epidemiology, pathophysiology, clinical presentation, assessment, and treatment of facial synkinesis.

Research into the epidemiology and risk factors of facial synkinesis is limited due to a lack of large databases tracking patients with facial palsy, inherent selection bias, and the wide range of symptom severity. Misguided nerve regeneration, polyneuronal innervation, and cortical changes are implicated in the development of synkinesis, and a better understanding of these mechanisms is required to develop new treatments. The clinical presentation of facial synkinesis varies considerably among patients, and important prognostic questions regarding timing of onset and progression of symptoms remain incompletely answered. Current management options for facial synkinesis include noninvasive modalities, chemodenervation, myectomy, and selective neurectomy. Potential new treatments for facial synkinesis are being investigated in animal models, but few have been tested in humans.

The treatment of facial synkinesis is currently hindered by limitations in clinical research and understanding of pathomechanism. Current studies predominantly yield level 4 evidence or lower. The development of large datasets of patients with facial palsy and the translation of basic science evidence to humans will facilitate the advancement of new treatments.