Applied Radiology

Prepared by Alan N. Brown, MD and Richard M. Silver, MD of the Department of Rheumatology, Medical University of South Carolina, Charleston, SC. CASE SUMMARY

A 10-year-old girl with a 7-year history of a chronic disease presented with pain localized to the left upper extremity. She had been engaged in a play session with her sibling and was being swung by the arms when an audible "snapping" sound was noted, followed by pain overlying the left bicep muscle.

DIAGNOSIS

Juvenile dermatomyositis with a fracture of soft-tissue calcinosis in the left biceps muscle

IMAGING FINDINGS

A radiograph of the left upper extremity shows linear intramuscular bands of calcification between the radius and the ulna. A linear, sharp, transverse lucency through a large calcium deposit in the biceps muscle is noted (Figure 1).

DISCUSSION

Juvenile dermatomyositis (JDM) is the most common idiopathic inflammatory myopathy (IIM) seen in children, constituting 85% of all cases of childhood IIM. ¹ The diagnosis of JDM requires the pathognomonic cutaneous findings of Gotton's papules or the heliotrope rash. ² The presence of these rashes distinguishes JDM from juvenile polymyositis. Evidence exists for a distinct immunologic pathogenesis for each of these two groups of childhood IIM. ³ Extramuscular manifestations of JDM include photosensitive rashes, arthritis, vasculitis, and involvement of the cardiac, pulmonary, and gastrointestinal systems. ⁴

Calcinosis (soft-tissue calcification) is common in JDM and has been reported to occur in 30% to 70% of children with the disease. ⁵ Risk factors for the development of calcinosis include delay from the onset of symptoms to initiation of therapy, a progressive disease course, trauma, and treatment with low doses of corticosteroids. ⁶ X-ray diffraction studies and electron microscopy have shown these soft-tissue calcification to be composed of hydroxyapatite. ⁷

Radiographic findings early in the course of JDM include muscle enlargement and the loss of the interface between muscle and subcutaneous fat. Muscle loss and joint contracture may follow. Calcinosis is most often seen in the proximal extremities on radiographic studies. Four distinct patterns of calcinosis have been described: linear intramuscular calcifications following fascial planes, deep nodular (tumoral), superficial nodular, and superficial reticular calcifications. Ultrasonography has demonstrated calcium-laden intramuscular fluid collections in some patients. ⁸ MRI findings include increased signal intensity on T2-weighted images of affected muscle, as well as perimuscular edema and enhanced chemical-shift artifact. Increased signal intensity is likewise seen in subcutaneous fat. Signal intensity of muscle returns to normal after successful therapy. ⁹

SUMMARY

This case represents a unique radiographic finding, ie, fracture of soft-tissue calcinosis, a common clinical manifestation of JDM. To our knowledge, a similar clinical scenario has not been reported in the medical literature.