A 63-year-old man presents with weakness and hemoptysis, but no fever, cough, or sputum. He has a 60-pack-per-year history of smoking. The chest x-ray (CXR) reveals a lung mass with mediastinal widening. On examination, there is a blue purple discoloration of the upper eyelids and erythema on his knuckles. He has proximal muscle weakness rated 4+/5, normal reflexes, and sensation. Which of the following is the most likely diagnosis for his muscle weakness?

This man has dermatomyositis, a paraneoplastic phenomenon of many cancers. The most common tumors associated with DM have been bronchogenic carcinomas, ovarian cancers, breast cancers, and melanoma but many others have occurred. The malignancy may antedate or postdate the myositis. Older age makes malignancy more likely. The extent of the workup for malignancy, if DM is the presentation, depends on clinical circumstances, but history and physical examination, not x-rays, are the cornerstones of evaluation.