Dermatomyositis in Children: MRI Findings

Childhood dermatomyositis is a multisystemic disease characterized by diffuse nonsuppurative inflammation of muscle fibers and skin. The disease affects blood vessels and is classified as a systemic vasculopathy.

Patients initially present with proximal lower extremity weakness, followed by proximal upper limb weakness and contractures. The skin lesions typically include discoloration of the upper lids and malar aspect of the face.

Radiographs and CT reveal sheet-like calcifications aligned along the planes of muscle and fascia in a symmetric distribution.

MR images reveal increased T2 signal in infarcted muscles affected by the vasculitis (yellow arrows) with edema in the fascial planes and subcutaneous fat. Children with dermatomyositis may also have extensive subcutaneous and intermuscular calcium-rich fluid collections (pink arrows), which can be differentiated from abscesses by the minimal peripheral enhancement seen in the former.

Muscle calcification, although rare, is more common in children, and occurs after a long evolution.

The main differential considerations are:

• Polymyositis: Has a similar distribution and MRI appearance, but affects an older age group. Edema-like abnormalities are said to be more common and muscle atrophy less common in dermatomyositis compared with polymyositis.
• Fasciitis:
• Infectious myositis: Asymmetric distribution. May have abscesses with peripheral enhancement.
• Muscle injury: Asymmetric muscular distribution
• Subacute muscle denervation:
• Radiation therapy: Asymmetric with with a well-delineated, sharp margin of abnormalities in the radiation field
• Rhabdomyolysis:

References

• Garcia J. MRI in inflammatory myopathies. Skeletal Radiol. 2000 Aug;29(8):425-38.
• Hernandez RJ, Sullivan DB, Chenevert TL, Keim DR. MR imaging in children with dermatomyositis: musculoskeletal findings and correlation with clinical and laboratory findings. AJR Am J Roentgenol. 1993 Aug;161(2):359-66.
• Chan WP, Liu GC. MR imaging of primary skeletal muscle diseases in children. AJR Am J Roentgenol. 2002 Oct;179(4):989-97.