Fibrodysplasia ossificans progressiva—a rare disease with distinctive features yet still a diagnostic challenge

Rationale: Fibrodysplasia ossificans progressiva (FOP) is rare genetic disease featuring progressive heterotopic ossification of soft tissues of the musculoskeletal system which leads to severe disability and premature death. Recognition of this disease is important since invasive diagnostic procedures can promote disease progression. However, despite its distinctive clinical manifestations, diagnosis can be difficult because of its rarity Patient concerns: A 20-year-old woman was referred to rheumatology clinic for management of “ankylosing spondylitis”. The patent had begun to have hard subcutaneous nodules when she was 1 year old, and subsequently developed hip joint pain and flexion contractures of knees and hips leading to disability. Diagnoses: Based on characteristic bilateral great toe deformities and radiographic images of ossification of soft tissues, a clinical diagnosis of FOP was made. This was confirmed by genetic test showing a heterozygous mutation (c.G617A) of the activin receptor 1A gene ( ACVR1 ). Interventions: The patient was treated symptomatically and with supportive measures, and her condition remained stable. Lessons: Diagnosis of FOP can be difficult, despite its distinctive clinical manifestations, because of its rarity. Recognition of this disease is important to avoid invasive diagnostic procedures which can promote progression.