Monoclonal B-cell lymphocytosis with renal involvement.

We report the case of a 70-year-old man with no relevant past medical history who presented with acute kidney injury. Kidney biopsy showed diffuse interstitial infiltration with typical chronic lymphocytic leukemia (CLL) phenotype B-cells. Subsequent studies revealed a normal lymphocyte count in the peripheral blood, and there was no evidence of lymphadenopathy or hepatosplenomegaly. Blood flow cytometry demonstrated a clonal B-cell population with a CLL phenotype. Without renal involvement, this case should be classified as monoclonal B-cell lymphocytosis. Renal function improved with steroid therapy. However, the patient developed CLL with significant lymphocytosis approximately two years later.