• Yian Guan and Dongyang Ma.
• Department of Orthodontics, School of Stomatology, Lanzhou University, Lanzhou, China.
• Medicine (Baltimore). 2024 Sep 13; 103 (37): e39648e39648.

RationaleMyositis ossificans (MO) is characterized by benign heterotopic ossificans in soft tissues like muscles, which can be classified into nonhereditary MO and fibrodysplasia ossificans progressiva (FOP). Nonhereditary MO is characterized by ossification of the soft tissues after acute or repetitive trauma, burns, or surgical intervention. FOP is a rare and crippling disease characterized by congenital malformation of the big toe and heterotopic ossification in muscle. The majority of FOP's musculoskeletal traits are associated with dysregulated chondrogenesis. The diagnosis is mainly based on clinical manifestation, imaging examination, and genetic analysis. There is still no effective treatment to cure or slow its progression. The best approach remains early diagnosis, conservative drug treatment, and injury prevention to avoid local ossification.Patient ConcernsA 34-year-old male presented at our hospital because of trismus caused by ossification of the masseter muscle. In addition, he had serious stiffness and multiple bony masses throughout the body, which led to limited movement.DiagnosesBased on the clinical manifestation of movement restriction, characteristic radiographic images of ossification of soft tissues, the genetic test showing a heterozygous molecule (c.974G > C, p.G325A) of the activin A receptor type I, the patient was diagnosed as FOP complicated with localized MO in masseter after trauma and infection.InterventionsThe patient underwent the surgical resection of ossification in the masseter muscle, he was instructed to insist on mouth-opening exercises and take glucocorticoids and nonsteroidal anti-inflammatory medications after surgery.OutcomesThe symptoms of trismus are relieved, and eating can be basically achieved after surgery, while the symptoms of trismus recurred 2 years later.LessonsAlthough FOP has unique clinical manifestations, its diagnosis may be difficult because of its rarity. Gene analysis is the main standard for diagnosis, while patients with different genotypic variations may show different clinical symptoms. Therapeutic interventions are still supportive and preventive, and surgery is not recommended except under certain circumstances.Copyright © 2024 the Author(s). Published by Wolters Kluwer Health, Inc.

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