Disseminated Extranodal Natural Killer/T-Cell Lymphoma Mimicking a Paraneoplastic Polymyositis

Abstract Extranodal natural killer/T-cell lymphoma (ENKTCL) is an aggressive EBV-associated non-Hodgkin lymphoma, most commonly arising from within the mucosa of the upper aerodigestive tract, typically with nasal presentation. Here, we present an interesting case of a 36-year-old man with ENKTCL with an atypical pattern of disease progression despite 3 cycles of SMILE chemotherapy. Restaging 18 F-FDG PET/CT demonstrated widespread uptake within the skeletal musculature in a distribution concerning for a paraneoplastic polymyositis. However, muscle biopsy confirmed ENKTCL dissemination.