Two cases of lysozyme-induced nephropathy with varying underlying diseases: myelodysplastic syndrome and chronic myelomonocytic leukemia.

Lysozyme-induced nephropathy (LyN) is a rare kidney complication associated with chronic myelomonocytic leukemia (CMML). This condition is characterized by distinctive pathological features, including granules within proximal tubular cells that stain positively with periodic acid-Schiff or lysozyme staining, and granular deposits identified as high-electron-density deposits under electron microscopy. Although CMML is the most common cause of LyN, previous reports have suggested that its occurrence may be associated with the myelodysplastic syndrome (MDS). This report describes cases of LyN in a patient with MDS and CMML. Although both the LyN cases, caused by either MDS or CMML, exhibited similar kidney pathological findings, there was a clinical difference in the occurrence of peripheral blood monocytosis. The MDS-induced LyN showed no persistent peripheral blood monocytosis and, when the bone marrow biopsy specimens were stained with lysozyme, numerous positive cells were observed. Thus, hematologic disorders wherein the bone marrow comprises lysozyme-producing cells may induce LyN, even without peripheral blood monocytosis.