Painful, Persistent Swelling Restricting Range of Motion in a Child

Manish Chadha, MS (Ortho); Vivek Kochar, MBBS

Disclosures

September 28, 2016

An early finding in patients with FOP is stiffness of the neck due to associated anomalies of the cervical spine. This can precede the appearance of heterotopic ossification at that site. Deformity of the great toes, such as shortened toes and hallux valgus, is characteristically present in all patients with FOP.[5] Other associated skeletal anomalies include short malformed thumbs, clinodactyly, short and broad femoral necks, and proximal medial tibial osteochondromas. Ankylosis of the jaw and rigid fixation of the chest wall can lead to serious complications such as severe weight loss and complications of rigid fixation of the chest wall. Most patients are confined to a wheelchair by the third decade of life and require lifelong assistance in performing activities of daily living.[7]

FOP must be distinguished from other genetic conditions of heterotopic ossification as well as from nonhereditary heterotopic ossification. Progressive osseous heteroplasia is a rare genetic condition of progressive ectopic ossification.[8] The presence of congenital malformation of the great toes, preosseous tumorlike inflammation or flare-ups, and the lack of cutaneous ossification differentiates FOP from progressive osseous heteroplasia.

Nonhereditary heterotopic ossification follows trauma or other injury in most cases. It can occur at any age but is rare in children younger than 10 years. Other differentials to be considered are aggressive juvenile fibromatosis, isolated congenital malformations, juvenile bunions, brachydactyly, lymphoma, desmoid tumor, and soft tissue sarcoma. About 60%-70% of individuals with FOP are misdiagnosed worldwide, leading to unnecessary and harmful diagnostic biopsies that exacerbate the progression of the condition (especially in the neck, back, or jaw, wherein asymmetric heterotopic ossification can lead to rapidly progressive spinal deformity, exacerbation of thoracic insufficiency syndrome, or rapid ankylosis of the temporomandibular joints).[7]

Routine biochemical evaluations of bone mineral metabolism are usually normal, although the serum alkaline phosphatase activity and the erythrocyte sedimentation rate may be increased (especially during disease flare-ups). Imaging modalities, such as radiography, bone scanning, CT scanning, and MRI, help in confirming the diagnosis; however, the definitive diagnosis of FOP can be made by simple clinical evaluation that associates rapidly appearing soft tissue lesions with malformations of the great toes. Definitive genetic testing for FOP is now available.[9] Clinical suspicion of FOP early in life on the basis of malformed great toes can lead to an early clinical diagnosis, confirmatory diagnostic genetic testing (if appropriate), and the avoidance of harmful diagnostic and treatment procedures.

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