18F-FDG PET detection of unknown primary malignancy in dermatomyositis.

Dermatomyositis is an inflammatory myopathy that has an association with malignancy in adults. We present a patient who initially presented with adenopathy and progressive muscular weakness and was diagnosed with dermatomyositis and lung carcinoma on further investigation. Whole-body PET/CT scan revealed diffuse proximal muscle hypermetabolism representing the inflammatory nature of dermatomyositis, and an intensely FDG-avid primary right lower lung small cell lung carcinoma and metastatic thoracic lymphadenopathy. PET/CT imaging may offer an "all-in-one" procedure as an alternative to other diagnostic procedures, reducing the number of unnecessary investigations in patients presenting with paraneoplastic syndromes searching for underlying malignancy.