Effect of Weakening of Ipsilateral Depressor Anguli Oris on Smile Symmetry in Postparalysis Facial Palsy

IMPORTANCE: Aberrant depressor anguli oris (DAO) activity may arise after recovery from acute facial paralysis and restrict movement of the oral commissure. OBJECTIVE: To quantify the degree to which DAO inhibition affects smile dynamics and perceived emotional state. DESIGN, SETTING, AND PARTICIPANTS: In this prospective, pretest-posttest study performed at an academic tertiary referral hospital, patients with unilateral postparalysis facial palsy were studied from January 16 through April 30, 2016. INTERVENTIONS: Local anesthetic injection into the ipsilateral DAO. MAIN OUTCOMES AND MEASURES: Healthy- and paretic-side commissure displacements from the midline lower vermillion border referenced to the horizontal plane were calculated from random-ordered photographs of full-effort smile before and after injection, and random-ordered hemifacial photographs of the paretic side were assessed as expressing positive, negative, or indiscernible emotion. RESULTS: Twenty patients were identified as having unilateral postparalysis facial palsy with marked synkinesis of the ipsilateral DAO. Patient mean age was 46 years (range, 24-67 years), with a male to female ratio of 1:3. Mean paretic-side commissure displacement increased from 27.45 mm at 21.65° above the horizontal plane to 29.35 mm at 23.58° after DAO weakening (mean difference, 1.90 mm; 95% CI, 1.26-2.54 mm; and 1.93°; 95% CI, 0.34°-3.51°; P < .001 and P = .20, respectively). Symmetry of excursion between sides improved by 2.00 mm (95% CI, 1.16-2.83 mm; P < .001) and 2.71° (95% CI, 1.38°-4.03°; P < .001). At baseline, observers assessed 7 of 20 paretic hemifaces (35%) as expressing positive emotion; this proportion increased to 13 of 20 (65%) after DAO weakening (P = .03). CONCLUSIONS AND RELEVANCE: Ipsilateral DAO weakening results in significant improvements in smile dynamics and perceived expression of positive emotion on the paretic hemiface in postparalysis facial palsy. A trial of DAO weakening should be offered to patients with this disfiguring complication of Bell palsy and similar facial nerve insults. LEVEL OF EVIDENCE: 3.