A case of lysozyme-induced nephropathy with improved renal function following treatment for chronic myelomonocytic leukemia.

Chronic myelomonocytic leukemia (CMML) is a myelodysplastic/myeloproliferative neoplasm characterized by persistent peripheral blood monocytosis. Although renal involvement can occur in patients with CMML, it may be overlooked. In addition, renal impairment is not included among the current criteria for initiating treatment for CMML.We report the case of a 75-year-old man with lysozyme-induced nephropathy that was initially considered to be diabetic nephropathy. He had a 20-year history of diabetes mellitus and presented to our hospital with weight loss and progressive anemia. After further evaluation, he was diagnosed with CMML. However, CMML-directed therapy was not initiated because he did not meet the treatment criteria, and he was managed with supportive care. At that time, renal dysfunction was already present, with an estimated glomerular filtration rate [eGFR] of 36.6 mL/min/1.73 m2, but it was attributed to diabetic nephropathy. Renal function subsequently deteriorated, and non-albumin-dominant proteinuria was observed. Kidney biopsy revealed lysozyme-induced nephropathy. Disease-directed therapy for CMML was initiated with the aim of preserving renal function. Treatment of the underlying disease resulted in improvement in renal function (eGFR 10.2 to 17.8 mL/min/1.73 m2), thereby avoiding dialysis despite advanced kidney failure. This case highlights the importance of considering lysozyme-induced nephropathy in the differential diagnosis when renal dysfunction occurs in patients with myeloid neoplasms accompanied by monocytosis. Furthermore, renal involvement in CMML may represent a clinically significant organ manifestation that can justify CMML-directed therapy, even when conventional hematological indications for treatment are not met.