Acute interstitial nephritis with polyclonal B cell infiltration and development of mantle cell lymphoma

A 69-year-old man with proteinuria, hematuria and abnormal renal and hepatic function developed acute renal failure. His clinical and laboratory examinations showed splenomegaly, edema, anemia and polyclonal hypergammaglobulinemia with high IgG levels. Renal biopsy showed interstitial nephritis with predominant B cell and plasma cell infiltration without monoclonality. After corticosteroid treatment, the patient showed remission in clinical symptoms and laboratory findings. However, one year later, he developed mantle cell lymphoma (MCL) with typical lymphocyte markers of cyclin D1 and CD5. When evaluated retrospectively, this patient appeared to have multicentric Castleman's disease initially and developed MCL later.