A 78-year-old man had fatigue and appetite loss for 5 months. He had been receiving low-dose methotrexate for rheumatoid arthritis. Computed tomography revealed multiple pulmonary infiltrations and muddiness of the fatty tissue surrounding the right kidney, ureter wall thickening, and hydroureter/nephrosis, which were suspected retroperitoneal fibrosis. Lung biopsy revealed polymorphic/lymphoplasmacytic lymphoproliferative disorder. Methotrexate withdrawal resulted in spontaneous regression. Therefore, retroperitoneal lesion may account for the diagnosis as having retroperitoneal lymphoproliferative disorder, not retroperitoneal fibrosis.
Keywords: Lymphoproliferative disorder; Methotrexate; Retroperitoneal fibrosis.