Atypical Fibrodysplasia Ossificans Progressiva Without Great Toe Malformation: A Diagnostic Challenge Preventing Unnecessary Surgical Intervention

Fibrodysplasia ossificans progressiva (FOP) is an exceptionally rare and disabling genetic disorder clinically characterized by malformed great toes and progressive heterotopic ossification of soft tissues. Diagnosis of FOP requires generic confirmation by the presence of ACVR1 mutation. We describe the case of a 12-year-old girl who presented without malformed great toes but developed restricted hip movement after minor trauma, followed by soft tissue swelling and impaired mobility of the lumbar spine, cervical spine, and shoulders several months later. Radiographic imaging revealed heterotopic ossification adjacent to the left greater trochanter, without underlying skeletal abnormalities. Genetic analysis confirmed a heterozygous pathogenic mutation in the ACVR1 gene (c.617G>A, p.Arg206His). The diagnosis of FOP prompted reconsideration of the previously planned surgery for hip stiffness relief, given the known risk that surgical procedures may trigger disease flare-ups and additional heterotopic ossification. During follow-up, the patient experienced recurrent flare-ups characterized by localized swelling, which responded well to high-dose corticosteroid therapy and supportive anti-inflammatory management. Management focused on minimizing trauma, maintaining functional mobility, and avoiding invasive procedures known to exacerbate disease progression. Preventive strategies and timely intervention during flare-ups are essential to preserving the quality of life in affected individuals. This case highlights the importance of early clinical suspicion in atypical presentations of FOP, which may help clinicians avoid unnecessary surgical procedures that could potentially exacerbate heterotopic ossification. Early recognition and a multidisciplinary approach are essential for optimizing patient outcomes and preserving functional mobility. Level of Evidence: Diagnostic Level V. See Instructions for Authors for a complete description of levels of evidence.