To summarize the complications and prevention after botulinum toxin type A(BTA) injection for masseter muscle hypertrophy(MMH).

The clinical data of patients with masseter hypertrophy who received BTA injection in Shanxi Bethune Hospital from January 2019 to September 2021 were retrospectively analyzed. Injection method: 100 U BTA was prepared into a solution with a concentration of 50 U/ml with 2 ml 0.9% sodium chloride injection. The "safe injection zone" of the masseter muscle was marked. The anterior and posterior boundaries were the anterior and posterior edges of the masseter muscle, respectively. The upper boundary was the line from the corner of the mouth to the earlobe, and the lower boundary was the lower edge of the mandible. The injection points(3 or 4 points) were at least 1 cm away from the four borders, and 25-40 U was injected on each side. The patients were followed up after treatment, the types of complications were recorded, and the treatment measures were summarized.

A total of 160 patients were enrolled, including 8 males and 152 females, with a mean age of (30.6±6.2) years. All patients were followed up for 1 to 6 months. The masseter muscle of all patients was reduced to varying degrees, the lower facial lines were softer, and the facial contour was improved. The incidence of complications was 81.3%(130/160). There were four main types of complications: (1) Complications with a nonmuscular etiology include ecchymosis in 5 cases (3.1%) which resolved spontaneously in 5 to 7 days and headache occurred in 2 cases (1.3%) which disappeared in 2-3 days with proper rest. (2) The complication related to the toxin effect mainly was the decrease of masticatory power in 86 cases (53.8%), which gradually recovered with the drug metabolism for 3-12 weeks. (3) Dose-related complications include facial ptosis in 4 cases (2.5%) with 30-40 U dose per side. 2 cases without special treatment, gradually recovered in about 8-12 weeks. One patient underwent the BTA injection to raise the mandibular margin and gradually recovered about 2 weeks later. One patient recovered gradually with the treatment by Thermage in another hospital. There were 9 cases (5.6%) of paradoxical rigid masseter muscle bulge. 5 cases resolved within 1 week after supplementary injection of 4 U botulinum toxin, and the other 4 cases resolved spontaneously within 1 to 2 weeks without special treatment. (4) Complications related to the injection site include abnormal smiles in 3 cases (1.9%). Patients were instructed to practice the smile correctly and gradually recovered in 4-12 weeks. Twenty-one patients (13.1%) had sunken cheeks. One patient improved by injection of hyaluronic acid, and the other patients recovered gradually within 8-12 weeks without special treatment.

The incidence of complications after BTA injection for MMH is high, and the manifestations are diverse. The injection should be performed in the recommended safe area of the masseter muscle. A reasonable dose and depth of injection can reduce the occurrence of complications.

Botulinum toxins; Masseter; Complications