Sequelae after Facial Palsy : Clinical, Anatomical and Electrophysiological Studies

Abstract: Background: Sequelae after peripheral facial palsy, which among others include synkinesis, non-functional smile and/or lower lip asymmetry, may be devastating for the patient. Bell’s palsy is the most common form of peripheral facial palsy. Aim: The aim was to study a) frequency and potential predictive factors of synkinesis in Bell’s palsy b) new surgical treatment options after facial nerve injury c) coactivation between muscles innervated by the facial nerve and the most common donor nerves in smile reanimation d) anatomical features of the lower lip depressors. Methods: I: Frequency, severity and early predictors of synkinesis development were studied in 829 Bell’s palsy patients. II and IV: Anatomical technical feasibility of intra-facial nerve transfers was analyzed. V: Anatomical features of lower lip depressor muscles were studied and a literature review for lower lip depressor myectomies was performed. III: Coactivation of muscles innervated by cranial nerves during voluntary facial movements was measured with electromyography. Results: I: In Bell’s palsy, synkinesis frequency was 21.3% at 12-months and Sunnybrook composite score at one month was found to be a good predictor for synkinesis. II and IV: A tension-free oculo-zygomatic and platysma-marginal mandibular nerve transfer was anatomically feasible. Full recovery of the lower lip after platsysma-marginal mandibular nerve transfer was found in a clinical case. III: The masseter muscle had a narrower coactivation pattern compared to the tongue. Bite induced a strong coactivation in the zygomaticus major muscle. V: The width of the depressor labii inferioris was 20 ± 4 mm and the distance from the midline to the lateral muscle border was 32 ± 4 mm. For the depressor anguli oris muscle, the corresponding measurements were 14 ± 3 mm and 54 ± 4 mm. The mean recurrence rate after lower lip myectomy reported in the literature is 21%.  Conclusion: I: Synkinesis in Bell’s palsy was 21%. Sunnybrook composite score at one month is a good predictor for synkinesis. II: Oculo-zygomatic nerve transfer may be a suitable technique to reduce eye synkinesis and achieve a stronger smile. III: The narrow coactivation pattern in the masseter muscle may be advantageous for spontaneous smile development. IV: The platysma motor nerve transfer is a feasible procedure and can lead to full recovery in lower lip paralysis. V: Knowledge of the width of the depressor muscles is of importance to ensure complete resection in lower lip myectomy.