Dermatomyositis (DM) or polymyositis (PM) are possibly considered to have an association with malignancies. We describe a case of dermatomyositis in which $^{18}F$-fluorodeoxy glucose (FDG)positron emission tomography (PET) was able to detect cancer recurrence earlier than any other modality in a patient with a history of primary pleural lymphoma, a very rare condition of malignancy. Further, a typical finding of dermatomyositis is diffuse hypermetabolism in the bilateral proximal shoulder and pelvic girdle areas was shown on $^{18}F$-FDG PET, which can implicate the inflammatory process in the skeletal muscle in dermatomyosistis. This case well illustrates the characteristic $^{18}F$-FDG findings of dermatomyositis as well as a capability of $^{18}F$-FDG PET in detection of recurrence of lymphoma, even in a rare condition.