Literature review of the adverse events associated with botulinum toxin injection for the masseter muscle hypertrophy.

[BACKGROUND] Masseteric hypertrophy is a benign condition characterized by the enlargement of the masseter muscles. A square-shaped jawline due to masseter muscle prominence or hypertrophy is one of the general characteristics of the Asian face, making it a frequent target for esthetic treatment requests. While the application of botulinum toxin on the masseter muscle is an off-label use, it is very popular in Asian countries. However, comprehensive reviews of the complications associated with this procedure remain limited in scope.

[OBJECTIVES] The goal of this study is to help physicians achieve a comprehensive understanding of the complications associated with neuromodulator injection over the masseter muscle via a thorough literature review.

[METHODS] A literature search was performed on the PubMed/MEDLINE, Google Scholar, and Science Direct databases using the search terms botulinum toxin, masseter hypertrophy, masseteric hypertrophy, and/or masseter hyperplasia. Literature from January 1994 to February 2018 was deemed to be allegeable for inclusion and analysis. All available prospective and retrospective studies, case series, case reports, and expert reviews were included, with an emphasis on types of complications, incidence rate, onset time, recovery time, and product used. Articles that do not mention side effects, complications, or adverse events were excluded.

[RESULTS] Thirty-six articles were found, covering type, incidence rate, and clinical course of the complications. These studies were summarized into tabular form for easy reference and comparison.

[CONCLUSION] Botulinum toxin masseter injections are commonly performed procedures with good results and safety profiles. The majority of complications appeared within 2-4 weeks of injection and disappeared within 12 weeks. Despite the temporary nature of these complications, they often decrease patient satisfaction and confidence, so physicians should familiarize themselves with the regional anatomy and injection safety zones.