Pediatric Fibrodysplasia Ossificans Progressiva (Myositis Ossificans) Clinical Presentation

Updated: Aug 14, 2018
  • Author: Robert J Pignolo, MD, PhD; Chief Editor: Lawrence K Jung, MD  more...
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  • Individuals with fibrodysplasia ossificans progressiva (FOP) appear normal at birth except for characteristic malformations of the great toes, which are present in all classically affected individuals. [19]

  • Episodic, painful soft tissue swellings or exacerbations usually develop in the preteen years. [9]

  • Although some exacerbations spontaneously regress, most transform soft connective tissues (including aponeuroses, fascia, ligaments, tendons, and skeletal muscles) into mature bone.

  • Minor trauma (eg, intramuscular immunizations; mandibular blocks for dental work; muscle fatigue; blunt muscle trauma from bumps, bruises, falls) or influenza-like viral illnesses can trigger painful new flare-ups of fibrodysplasia ossificans progressiva, leading to progressive heterotopic ossification (HO).

  • Most patients with fibrodysplasia ossificans progressiva are confined to a wheelchair by the third decade of life and require lifelong assistance in performing activities of daily living.

  • The severe disability of fibrodysplasia ossificans progressiva results in low reproductive fitness.



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  • Two clinical features define classic fibrodysplasia ossificans progressiva: malformations of the great toes and progressive heterotopic ossification.

  • Among patients with fibrodysplasia ossificans progressiva–like HO and/or toe malformations, a small number of patients have clinical features unusual for fibrodysplasia ossificans progressiva. [5] These atypical fibrodysplasia ossificans progressiva patients are categorized as fibrodysplasia ossificans progressiva–plus (classic defining features of fibrodysplasia ossificans progressiva plus one or more atypical features) and fibrodysplasia ossificans progressiva variants (major variations in one or both of the 2 classic defining features of fibrodysplasia ossificans progressiva, such as normal great toes or severe reduction deficits of digits).

  • Heterotopic bone replaces skeletal muscle and connective tissues.

  • Heterotopic ossification in fibrodysplasia ossificans progressiva progresses in characteristic anatomic and temporal patterns that mimic the patterns of normal embryonic skeletal formation. Heterotopic ossification is typically seen first in the dorsal, axial, cranial, and proximal regions of the body and later in the ventral, appendicular, caudal, and distal regions.

  • Several skeletal muscles, including the diaphragm, tongue, and extraocular muscles, are spared from fibrodysplasia ossificans progressiva. Cardiac muscle and smooth muscle are also spared from heterotopic ossification.

  • Stiffness of the neck is an early finding in most patients and can precede the appearance of heterotopic ossification at that site.

  • Characteristic anomalies of the cervical spine include large posterior elements, tall narrow vertebral bodies, and fusion of the facet joints between C2 and C7. [10] Although the cervical spine often becomes ankylosed early in life, any minimal residual movement may eventually result in painful arthritic symptoms.

  • Other skeletal anomalies commonly associated with fibrodysplasia ossificans progressiva include short malformed thumbs, clinodactyly, short broad femoral necks, and proximal medial tibial osteochondromas. [11]

  • Severe weight loss may result following ankylosis of the jaw.

  • Pneumonia and right-sided heart failure are complications of rigid fixation of the chest wall.