Lysozyme Nephropathy: An Underdiagnosed Cause of AKI

Introduction: Lysozyme Nephropathy (LyN) is a rare and under-recognized cause of Acute Kidney Injury (AKI) in patients with hematologic malignancies. It is typically associated with Chronic Myelomonocytic Leukemia (CMML) due to overproduction of lysozyme by tumoral cells leading to proximal tubular cell injury. It is extremely rare, but, to-date reported cases in literature have demonstrated a wide spectrum and prognosis. Here we present a case of lysozyme nephropathy which was diagnosed at the same time as CMML and had renal recovery due to early diagnosis and timely initiation of treatment. Case Description: 70 yo M with PMH of DM, chronic colocutaneous fistula and COPD presented to the hospital due to abnormal outpatient labs. Patient complained of black urine for 1 wk. Outpatient labs showed WBC 106.5 x 10(3)/uL with diff 37% neutrophils, 10% bands, monocytes, and ~11% blasts. Hb was 6.3 mg/dL, platelet count 212 x 10(3)/uL , and Cr 3.35 mg/dL up from baseline of 1.0 mg/dL. UA showed >50 RBCs/hpf, 2+ proteinuria, UPCR was 1.46 g/g and renal USG showed no obstructive nephropathy. CT A/P showed splenomegaly of 18 cm. Due to worsening renal function, patient was started on hemodialysis (HD) and underwent renal biopsy which was significant for tubular injury with LyN. Bone marrow biopsy was performed and showed markedly hypercellular marrow with myeloid and megakaryocytic hyperplasia, with erythroid hypoplasia and dysmegakaryopoiesis. Flow cytometry revealed CD34 positive myeloid blasts around 3% of the cells. FISH analysis was positive for trisomy 8 but negative for BCR-ABL t(9;22), karyotypes 47 XY+8[20] confirming the diagnosis of CMML. Patient was treated with hydroxyurea and azathioprine. He had partial renal recovery within 4 weeks of initiating treatment and HD was discontinued. Discussion: Lysozyme is a bactericidal enzyme synthesized in large amounts by neoplastic monocytes. LyN is seen in diseases with increased monocyte turnover such as underlying hematologic disorders. Although, few cases have been reported in literature, there is still paucity of awareness of this condition. Reporting of our case would add to the literature and improve awareness of LyN, hence leading to prompt diagnosis and treatment.