The management of acute peripheral facial nerve palsy is complex, challenging, and controversial. This article focuses on the management of acute, unilateral, idiopathic facial nerve palsy, more commonly known as Bell’s palsy. The annual incidence of Bell’s palsy is 20 to 30 per 100,000 population, and facial weakness generally resolves in six months either with medical treatment or by observation alone. However, a small subset (10%–29%) of affected individuals display persistent facial nerve dysfunction. These patients can suffer from corneal abrasions, dysarthria, facial contracture, synkinesis, and the social-psychological challenges of facial asymmetry.
The cause of Bell’s palsy is by definition uncertain, but evidence implicates facial nerve edema due to viral infection. Swelling within the narrow bony confines of the fallopian canal leads to damage, with the meatal foramen and labyrinthine segments common sites of conduction block in cases taken to surgery. The actual extent of nerve damage varies significantly, with some patients showing only mild weakness and others permanently disfigured. Ideal assessment of Bell’s palsy patients would allow the clinician to definitively identify patients who will not regain full facial nerve function; unfortunately, such a test does not exist. A variety of useful assessments do exist however, including electrodiagnostic and function-based (House-Brackmann [HB] and Yanagihara grading systems) evaluations. This article discusses the prognostic implications of electroneurography (ENoG), a tool that provides reliable objective measurements of facial nerve function in acute facial nerve palsy.
The course of Bell’s palsy varies, with a minority of patients suffering significant residual facial weakness. Several studies confirm the prognostic value of ENoG testing performed between three and 14 days after onset of complete facial paralysis. In those patients who do not exceed 90% degeneration, use of ENoG is useful as a prognostic tool to reassure patients of the high likelihood of recovery to acceptable (HB I or II) facial function. In patients with an ENoG response exceeding 90% degeneration, and who show no voluntary EMG motor unit potentials, surgical decompression by a qualified surgeon likely offers improved functional outcomes. One recent study suggests 85% degeneration is predictive of unfavorable outcomes; however, this remains to be validated by further studies. Read the full article in The Laryngoscope.