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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.