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Myositis-specific autoantibodies are relevant factors that define the disease phenotype of dermatomyositis (DM). Anti-Mi-2 antibody-positive DM patients may present with the typical skin lesions and prominent myositis. On the other hand, adult DM patients with anti-TIF-γ antibody seem to be associated with internal malignancy. Here, we report a rare case of juvenile dermatomyositis (JDM) exhibiting anti-Mi-2 and antitranscriptional intermediary factor-1 gamma (TIF1-γ) antibodies, with no internal malignancy. A 16-year-old female Japanese patient under treatment with a 2-year history of chronic eczematous lesions was admitted to our department with elevated levels of muscle enzymes. Characteristic skin changes, such as Gottron's papules of the hand, heliotrope rash of the eyelids, and poikiloderma-like legions and diffuse pigmentation on the back, were observed. Histologically, the patient's skin was characterized by the presence of lymphocytic vascular inflammation and endothelial swelling, which are consistent with DM. Severe symmetric proximal muscle weakness, elevated serum muscle enzymes and the presence of anti-TIF1-γ and Mi-2 antibodies were noted. The diagnosis of JDM was made according to the European League Against Rheumatism (EULAR) diagnostic criteria. A high dose of corticosteroids and following intravenous cyclophosphamide treatment (750 mg three times) resulted in an improvement in clinical manifestations and functional outcomes, and recurrence did not occur. Estimation of autoantibodies may serve as an ancillary tool in delineating and defining distinct clinical phenotypes in JDM.

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