Three different CT and FDG PET/CT findings of pulmonary involvement in methotrexate‐associated lymphoproliferative disease

Lymphoproliferative disease (LPD) is one of the complications of methotrexate (MTX) therapy. In MTX‐associated LPD (MTX‐LPD), LPD lesions limited to the lungs are rare and show various types of opacity. A 75‐year‐old woman with rheumatoid arthritis (RA) presented with myalgia. She had been taking MTX for 11 years. Chest computed tomography (CT) scans showed a nodule in the left lower lobe that had grown significantly and a new nodule in the right lower lobe. 18F‐fluorodeoxyglucose (FDG)/positron emission tomography (PET)/CT revealed significant FDG uptake in these nodules. Transbronchial biopsy specimen showed diffusely distributed CD20‐positive lymphoid cells, and we made a diagnosis of MTX‐LPD. All lung lesions disappeared within months after the immediate discontinuation of MTX. We also had two other patients with MTX‐LPD lung lesions that had high FDG uptake. FDG PET/CT might be a useful diagnostic tool as it may reflect disease progression and help identify separate lesions.