Juvenile dermatomyositis

A 2-year-old female patient presented with fever and petechial rash over both lower limbs for 1 month. She developed facial puffiness and pedal oedema. She further complained of lower limb pain and weakness for 5 days.

On clinical examination there was bilateral pedal oedema with petechiae, and hepatomegaly. Bulk, tone and power of the lower limb muscles were normal. There was no evidence of other skin lesions. Peripheral smear showed a leukoerythroblastic picture. Dengue, leptospiral and salmonella antibodies were negative. EMG was suggestive of a myopathic pattern with membrane instability, and creatinine kinase levels were 846.6 U/L. Chest X-ray showed air space opacity in both lung bases. MRI showed diffuse T2/STIR hyperintensity involving the muscles and subcutaneous tissues of the thigh. The abdominal aorta and its branches showed no stenosis or aneurysm. Muscle biopsy was performed and a confirmatory diagnosis of dermatomyositis was made.

Dermatomyositis is an autoimmune condition with a female predilection (2.3:1 to 5:1) and bimodal distribution (5-14 years and 45–64 years). Inflammatory myopathies are classified as a) idiopathic and b) secondary, of which idiopathic inflammatory myositis is the most common [1]. 30-70% of patients can have calcification. It can present in two forms, a) juvenile dermatomyositis (JDM), which affects children (5-14 years) and tends to be more severe, and b) adult dermatomyositis (ADM), which typically affects adults around the age of 50 years. It can affect various other organs such as heart, lung and GI tract. These patients present with elevated muscle enzymes (CK) and elevated muscle specific antibodies (anti-RNA and anti-Mi2). The condition can be associated with interstitial lung disease and malignancy. Rarely the condition can cause death [2]. On imaging radiographs show dystrophic calcification in muscles and soft tissues classically seen affecting the thigh region. Chest radiography may show diaphragmatic elevation. Acroosteolysis may also be seen. MRI is useful as a guide in planning biopsy from involved muscle groups [3]. Advanced MRI techniques like T2 mapping and spectroscopy help in the diagnosis of the condition [4]. Diagnosis is made based on clinical features, muscle enzyme levels, imaging, and biopsy [5]. On MRI T2-weighted fat saturated sequences are mainly used to eliminate fat and demonstrate oedema. T1-weighted sequences clearly depict fatty degeneration. During the acute phase MRI shows STIR hyperintensity and post-contrast enhancement in the involved muscle group, and during the chronic phase shows fatty atrophy of muscle and subcutaneous tissue [5].

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