Non-traumatic myositis ossificans circumscripta: A diagnosis trap

Abstract

Myositis ossificans circumscripta (MOC) is a benign condition of non-neoplastic heterotopic bone formation in the muscle or soft tissue. Trauma plays a role in the development of MOC, thus, non-traumatic MOC is very rare. Although MOC may occur anywhere in the body, the lesions are localized predominantly in the high-risk sites of injury, such as the thigh, buttock, and elbow. MOC can easily be mistaken for osteomyelitis or a malignant tumor, specifically osteosarcoma or soft-tissue sarcoma. We report a rare case of non-traumatic myositis ossificans circumscripta of thigh which appear clinically and radiologically as a malignant neoplasm. Despite its rarity, MOC should be contemplated in the differential diagnosis of malignant tumors.

Non-traumatic myositis ossificans circumscripta

“…Myositis ossificans circumscripta is a benign, self‐limiting, heterotopic metaplastic ossification usually confined to a single muscle or muscle group . MOC is not a premalignant lesion…”

“…The aetiology and pathogenesis of MOC remains unclear although approximately 75% of all cases of MOC develop secondary to muscular trauma . Men and women are equally affected, with approximately 80% of cases arising in the large muscles of the extremities, most commonly the thigh . It is most common in active men in the second and third decade of life .…”

“…Myositis ossificans circumscripta (MOC) is an inflammatory pseudotumour characterised by the aberrant formation of bone in extraskeletal soft tissues, usually occurring after muscle injury . In rare cases, the condition can occur in the absence of a traumatic injury . In such cases, the disease is clinically and radiologically difficult to distinguish from soft tissue malignancy …”

“…In rare cases, the condition can occur in the absence of a traumatic injury . In such cases, the disease is clinically and radiologically difficult to distinguish from soft tissue malignancy …”

An atypical presentation of myositis ossificans

“…The most important differential diagnosis is extra-skeletal osteosarcoma, which has similar clinical and pathological characteristics. [6][7][8] Various imaging techniques are available to evaluate the presence and progression of MO including musculoskeletal ultrasound (MSU), radiography, computed tomography, magnetic resonance imaging and skeletal scintigraphy. It is important to note that the radiologic features evolve as the lesion matures.…”