Fibrodysplasia (myositis) ossificans progressiva. Clinical lessons from a rare disease.

Fibrodysplasia (myositis) ossificans progressiva is a rare dominantly inherited disorder, in which defects in skeletal patterning particularly affecting the big toes, are associated with progressive endochondral ossification of the large striated muscles in a specific order leading to prolonged disability. A recent series of 28 patients studied for as many as 24 years exemplifies the presentation and course of this disease. Painful swelling of muscles (myositis) leading to ossification began at a mean age of 4.6 years (range, 0-16 years) initially in the neck and upper spine (in 25 subjects) and later around the hips, other major joints, and jaw. The rate and extent of disability was unrelated to the time of onset. No form of treatment produced consistent benefit. Despite the unique clinical features, the initial diagnosis of fibrodysplasia ossificans progressiva was often wrong and usually considerably delayed. Mistaken histologic diagnoses such as soft tissue sarcoma or fibromatosis could lead to inappropriate treatment.