Enhanced gain of blink reflex responses to ipsilateral supraorbital nerve afferent inputs in patients with facial nerve palsy

Abstract

Objectives: Patients with peripheral facial palsy (PFP) may present with transient hyperkinetic movement disorders in the side contralateral to the paralysis. One possible cause of such enhanced motor activity is sensitization of reflex responses to afferent inputs from the unprotected cornea. We hypothesized that if this sensitization occurs, the size of the orbicularis oculi (OOc) responses induced by afferents from the ophthalmic branch of the paralyzed side would be larger than those induced by afferents from the contralateral side. Methods: In 68 patients with complete PFP and in a group of 30 age-matched control subjects we recorded the response of the OOc muscle of one side to electrical stimulation of the supraorbital nerve of both sides, and calculated the ratio between R2c and R2 (R2c/R2). Results: The mean R2c/R2 ratio was significantly larger in patients than in control subjects (unpaired t test, P<0.05). Larger R2c than R2 responses were observed in 23.1% of control subjects and in 80.9% of patients ( χ 2=13.3, P<0.01). Conclusions: Our results suggest that patients with PFP have an enhanced blink reflex gain to inputs from the paralyzed side compared to those of the non-paralyzed side. Sensitization of the blink reflex polysynaptic pathways to inputs carried by afferent fibers from the ophthalmic branch of the paralyzed side can play a role in inducing an abnormal facial motor behavior after PFP.