[Contingent diagnosis of sarcoidosis by 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET) after completion of chemotherapy for malignant lymphoma].

A 55-year-old man with bilateral cervical lymphadenopathy was diagnosed with diffuse large B-cell lymphoma, stage IIA, and underwent sequential chemoradiotherapy (R-CHOP, 3 courses followed by 30 Gy cervical irradiation). Chemotherapy response was evaluated by 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET). 18F-FDG uptake of the primary lesion was completely diminished; however, a new paratracheal uptake was observed. FDG-PET-guided biopsy revealed sarcoidosis. Sarcoidosis with lymphoma is a rare condition, and it is difficult to distinguish early-stage sarcoidosis from lymphoma without biopsy. Routine FDG-PET significantly increases the detection of unexpected diseases. Physicians should perform biopsies of lesions or follow them carefully in lymphoma patients with unexpected 18F-FDG uptake.