[A case of progressive ossifying myositis caused by <i>ACVR1</i> gene mutation].

A 2-year-and-10-month-old boy presented with multiple masses in the neck and chest for over 3 months. The child had a history of unstable walking, with hard lumps visible at the injury sites after falls, which would resolve on their own. Following a recent injury, a mass was discovered in the posterior neck, protruding above the skin surface and accompanied by limited joint movement. Gradually, new masses were found on the left side of the neck, back near the scapular lower angle, in the scapular fossa, and along the left axillary midline. Magnetic resonance imaging examination showed diffuse low signal on T1-weighted images and high signal on T2-weighted images in the bilateral posterior neck and back muscles two months ago. A CT scan revealed muscle swelling, with areas of patchy low density and multiple nodular high-density ossifications within some muscles. Genetic testing results indicated a mutation in the <i>ACVR1</i> gene, leading to the final diagnosis of progressive ossifying myositis in this patient. This article summarizes the etiology, diagnosis, and treatment of one case of progressive ossifying myositis, providing a reference for clinicians.