The neuropathy of marginal mandibular branch of the facial nerve

Abstract

To analyze the diagnosis, treatment and rehabiltation of patients with marginal mandibular branch of the facial nerve (MMB). We have collected 6 patients (mean age 40 [33.8; 44] years) with isolated lesion of MMB that innervates the depressor labii inferioris and chin muscle. The illness duration without any improvement was 35 [13; 44] days. Diagnosis and treatment were carried out according to the special algorithm developed and implemented at the N.V. Sklifosovsky Research Institute of Emergency Medicine. With needle myography of the muscle that lowers the lower lip, the change in the ratio of the maximum amplitudes of the interference pattern (MAIP) in all patients exceeded 15%, and in 2 cases it was more than 90%. Comparing with the healthy face side, a change of the MAIP ratio less than 90% was considered as the biomarker of favorable prognosis, with conservative treatment recommendations, e.g. the set of exercises with targeted effects on depressor labii inferioris. With regular exercises, patients noted positive dynamics of restoring the symmetry of the smile in 1-2 months of the disease, full recovery - in 4-5 months. In case of exercises rejection, there was no positive dynamics. A change in the MAIP ratio more than 90% or the absence of motor unit potentials was considered as the biomarker of an unfavorable outcome and an indication for surgical treatment. After surgical treatment, the improvement occurred within 4-5 months. In conservative treatment group, there were no positive changes even with regular exercises. The diagnosis of an isolated lesion of MMB is established clinically using a protocol of step-by-step assessment of facial muscle function, and tactics is determined by needle myography with depressor labii inferioris. Even with favorable myographic predictors, spontaneous recovery may not occur, exercises with a targeted effect on the depressor labii inferioris are required, and in the presence of unfavorable predictors, surgical treatment is reccomended.