Anti-TIF1g antibody predicted malignancy of thymic tumor with dermatomyositis as an “autoimmune tumor marker”

Rationale: An association between inflammatory myopathy and malignancy has been recognized particularly in patients positive for anti-transcription intermediary factor 1g (TIF1g) antibody. We report a case of anti-TIF1g antibody positive dermatomyositis (DM) associated with thymic carcinoma which radiographically mimicked benign tumor. Patient concerns: A 72-year-old man presented typical characteristic cutaneous manifestations and proximal muscle weakness with elevated levels of myogenic enzymes. An anterior mediastinal tumor was detected by computed tomography (CT) scan and radiographically assessed to be benign with distinct borders and little enhancement. Diagnoses: DM with anti-TIF1g antibody and thymic carcinoma. Interventions: Thymic carcinoma was completely resected by surgery. DM was induced into remission with glucocorticoid treatment. Outcomes: The serum level of myogenic enzyme remained within normal range under low-dose glucocorticoid maintenance. No evidence of carcinoma recurrence with CT scan was observed at 1-year follow up. Lessons: The present case indicated that anti-TIF1g antibody would play a role as the “autoimmune tumor marker” in patients with inflammatory myopathy.