Age / Sex : /

Age / Sex : 27/F
C.C.: Right thigh pain, Bed-ridden status

fibrodysplasia(myositis) ossificans progressive

Discussion

Findings:
- MRI of the patient taken on the first visit to the hospital to evaluate thigh pain and swelling demonstrates diffuse and extensive edema and swelling of adductor and hamstring muscle groups.
 - Radiographs of whole body demonstrate florid ossification along the muscle, fascial plane, and along the insertion of ligaments and tendons generally.
- On spine radiographs, extensive fusion of vertebrae is seen with prominence of fusion at the posterior elements. Paravertebral soft tissue ossification is seen. Ossification of nuchal ligament is prominent on C-spine radiograph. Heights of all vertebrae are larger than AP diameter. On foot radiograph, extensive ossification around the 1st MTP joint with mild hallux valgus deformity is noted.

Differential Diagnosis:
1. Etiologies causing extensive metastatic ossification or calcification such as - Idiopathic calcinosis universalis - Dermatomyositis - Idiopathic tumoral calcinosis
2. Etiologies causing spinal fusion such as - Klippel-Feil syndrome - Still’s disease - Ankylosing spondylitis

Diagnosis: Fibrodysplasia (myositis) ossificans progressiva

Discussion:
== Clinical and Pathologic Perspective ==
  Fibrodysplasia ossificans progressive is an hereditary disorder characterized by asymmetric congenital anomalies of the great toes and thumbs and progressive chondrogenesis and heterotopic ossification of striated muscles, tendons, ligaments, fasciae, aponeuroses, and occasionally skin. Digital anomalies are at birth, but formation of bone is postnatal. The earliest pathologic abnormalities are edema and rapidly proliferating fibroblasts and myofibroblast in loose mucoid background in the involved tissues such as muscles, tendons, and ligaments. Mesenchymal proliferation then results in the formation of multifocal interconnecting nodules composed of spindle cells and basophilic collagen allowing deposition of calcium salts. Various stages of bone formation occur thereafter. Eventually, the entire tissue involved is replaced by columns or plates of lamellar bone which has identical histologic feature with normal bones except that it shows a few intact muscle fibers in it. Fibrodysplasia ossificans progressiva is a rare disease. By 1982, only 600 cases had been described in the literature. Although the onset of the symptoms usually is in the first decade of life, ossification rarely is present at birth. The mean age at onset is 3 years. The disease usually progresses from the shoulder girdle to the upper arms, spine, and pelvis. Diagnostic difficulty may be accentuated by failure to note the digital anomalies of the patient. The disease course is erratic remissions and exacerbations. A new episode of ossification frequently is precipitated by minor trauma, injections, or surgery, but the injury is not the primary problem and determines only the site of new ossification. Early death is inevitable. It may occur secondary to respiratory failure with constriction of the chest wall and, in many cased, pneumonia, or it may result from starvation with ossification of the masseter muscles.

== Radiographic Finding ==
  Digital abnormalities are present at birth, are symmetric, and in the vast majority of cases, precede the soft tissue ossification. The most common type of abnormality is a hallux valgus deformity associated with microdactyly of the 1st toe. Other congenital anomalies of the skeleton are hallux valgus deformities, broad femoral necks, bilateral thickening of the medial cortices of the tibiae, an abnormal carrying angle at the elbow. After the onset of symptoms, the radiographic findings in the individual locations are similar to those seen in the traumatic form of myositis ossificans. The first radiographic finding is a soft tissue mass. The lesion gradually shrinks in size and ossifies. The final appearance of the lesion may be that of a cylindrical column of solid new bone replacing the entire muscle of the neck and extremities or a plate of new bone with a dotted veil pattern outlining the fascial plane of the back and mandible. Involvement of the insertions of fasciae, ligaments, and tendons at metaphysic produce “pseudoexostosis”. Unlike true osteochondroma, no cortical continuity of the outgrowth with the adjacent bone is present. Abnormalities of the spine occur as a result of loss of motion. In the majority of cases, ossification of the soft tissues is followed by fusion of the posterior elements, and finally, in adult patients, fusion of the vertebral bodies. These finding can mimic appearance of ankylosing spondylitis. So called “dog-vertebrae” which are higher than they are wide occur as a result of limited weight bearing. The radiographic differential diagnosis includes the causes of metastatic calcifications such as aforementioned diseases, but in all of these conditions, the dense lesions remain calcific and do not mature into trabecular bone. In addition, the clinical history is totally different. In the cervical spine, other caused of fusion of the posterior elements can resemble this disease radiographically, but the presence of soft tissue ossification and digital anomalies greatly simplifies interpretation.

References:
1. Goldman AB. Heritable Diseases of Connective Tissue, Epiphseal Dysplasia, and Related Conditions. In: Resnick D eds. Diagnosis of Bone and Joint Disorders, 4th ed. Philadelphia, Pensylvania: W.B. Saunders Company, 2002:4409-4415