An unexpected cause of a febrile patient with huge splenomegaly.

We report an unexpected cause of a febrile patient with huge splenomegaly. A 32-year-old patient with fever and huge splenomegaly was admitted to our hospital. Diagnostic splenectomy revealed that the enlarged spleen adhered strongly to the abdominal organs. Pathologically, the splenic parenchyma showed no malignant cells, and the soft tissue adjacent to the splenic hilum showed a proliferation of fibroblastic or myofibroblastic spindle cells with fibrosis and lymphoplasmacytic infiltration. These findings lead to a diagnosis of peritoneal fibrosis, and an administration of 50 mg/day of prednisolone alleviated all the symptoms. The differential diagnosis of huge splenomegaly with fever usually includes hematolymphoid malignancies and infectious diseases; however, our case was diagnosed as idiopathic retroperitoneal fibrosis. Our case suggests that when we see patients with fever and huge splenomegaly, differential diagnosis should include retroperitoneal fibrosis.