Ultrasonic appearances of the early changes in fibrodysplasia ossificans progressiva

Progressive heterotopic ossification and congenital skeletal anomalies characterize the very rare and relentless condition of fibrodysplasia ossificans progressiva (FOP) or myositis ossificans progressiva (MOP)(McKusick, 1972). These patients frequently present with subcutaneous masses which are often painful (Lindhout & Golding, 1985) and therefore ultrasound may be used in the initial investigation. We report a case of FOP presenting with recurrent soft-tissue swellings and demonstrate the ultrasonic appearances not previously documented in this condition. A 5-year-old boy first presented with a history of pain in his right knee following a minor injury. Radiographs showed an apparent simple exostosis arising from the medial side of the proximal tibial metaphysis (Fig. 1); no further investigations were performed at this time. He presented again several months later with a swelling in the subcutaneous tissues of the left anterior thigh and with pain on walking. No soft-tissue abnormality was identified ...