Histiocytes Plugging the Glomerular Capillaries: A Rare Manifestation of Monoclonal Gammopathy

Abstract

Monoclonal gammopathy is a disorder characterized by the proliferation of plasma cells or B lymphocytes and overproduction of monoclonal immunoglobulin. Renal involvement in monoclonal gammopathy can manifest in various ways, but histiocytes obstructing glomerular capillaries is exceptionally rare. We report on a case of a patient presenting with renal impairment, proteinuria, and anemia. Kidney biopsy revealed numerous histiocytes plugging glomerular capillaries and renal tubular lumina, containing crystalline monoclonal immunoglobulin deposits. The bone marrow aspirate demonstrated an increase in atypical plasma cells with cytoplasmic inclusions, consistent with a diagnosis of multiple myeloma. This case highlights an unusual presentation of monoclonal gammopathy with renal involvement, emphasizing the importance of considering this diagnosis in patients with unexplained renal impairment and proteinuria. This is, to our knowledge, the fourth reported case of crystal-storing histiocytosis involving glomerular capillary loops and the first to describe its coexistence with light chain cast nephropathy.