Lysozyme

A 76-year-old Caucasian male with renal failure underwent renal biopsy. He had a serum creatinine of 2.1 mg/dl and a urine protein/creatinine ratio of 0.3.  SPEP showed hypergammaglobulinemia with a polyclonal increase, no monoclonal proteins were identified.  The patient has a past medical history of Chronic myelomonocytic leukemia (CMML). Despite the lack of significant proteinuria, the renal biopsy is characterized by proximal tubules that are stuffed with numerous brightly eosinophilic and silver negative protein resorption droplets (A). The droplets are weakly PAS-positive and strongly positive for lysozyme (B and C). These findings are consistent with lysozyme nephropathy. This is a disease that is most commonly found in association with CMML. It is important to know that lysozyme is normally positive in proximal tubule cytoplasm. However, the degree of staining is much stronger in cases of lysozyme nephropathy.