The condition produces painful lumps and stiffness in the adjoining joint. Lumps decrease in a few weeks, but joint mobility reduction persists. Exacerbating factors for ossifications at new sites include venipuncture, biopsy of lumps, IM injections, dental treatments, and excision of masses. The most common sites are the sternocleidomastoid muscle, paraspinal muscles, the jaw's masticatory muscles, and shoulder and pelvic girdle muscles. Spared are the abdominal muscles, extraocular muscles, and GI tract and tongue muscles.
Ossification progresses from proximal to distal and cranial to caudal.
Routine laboratory results may be within reference ranges. In myositis ossificans progressiva, ECG findings may be abnormal, while spirometry may demonstrate restrictive pattern. Plain radiography of nonhereditary myositis ossificans traumatica Early examination may be unremarkable. Floccular calcified density is observable in soft tissues at 2-6 weeks from onset. By 6-8 weeks, calcification becomes sharply circumscribed.