A case report of dermatomyositis with the missed diagnosis of non-small cell lung cancer and concurrence of pulmonary tuberculosis.

A 42-year-old man with four months of retrosternal pain and two months of skin rashes and proximal muscle weakness was diagnosed with dermatomyositis (DM) based on muscle enzyme analysis and needle electromyography. Chest computed tomography (CT) showed scattered inflammation nodules in both lungs' upper lobes with negative sputum smear for lung cancer and pulmonary tuberculosis (TB). A good clinical response to oral prednisone was obtained, except for the retrosternal pain in the preceding two months. Urgent CT pulmonary angiography ruled out pulmonary thromboembolism but revealed squamous cell lung cancer with metastases in the sternum and mediastinal lymph nodes. In retrospect, we found osteolytic destruction consistent with sternal metastasis on CT taken at the initial treatment of DM, which was missed by radiologists. Simultaneously, the man was diagnosed with pulmonary TB based on rapid mycobacterial TB detection. This case report indicates the radiologic errors and highlights the importance of a thorough search for underlying lung cancer and pulmonary TB in patients with DM, especially in countries with a high TB burden.