Glomerular
lipidosis is a rare histological feature presenting the extensive glomerular accumulation of
lipids with or without histiocytic infiltration, which develops under various conditions. Among its various etiologies,
macrophage activation syndrome (MAS) is a condition reported to be associated with histiocytic glomerular
lipidosis. Here we describe the first case of glomerular
lipidosis observed in a renal allograft that histologically mimicked histiocytic glomerulopathy owing to MAS.
CASE PRESENTATION: A 42-year-old man underwent successful living-donor
kidney transplantation. However, middle-grade
proteinuria and increased serum
triglyceride levels indicative of
type V hyperlipidemia developed rapidly thereafter. An allograft biopsy performed 6 months after the
transplantation showed extensive glomerular infiltration of CD68+ foam cells (histiocytes) intermingled with many CD3+ T-cells (predominantly CD8+ cells). Furthermore, frequent contact between glomerular T-cells and histiocytes, and the existence of activated CD8+ cells (CD8+, HLA-DR+ cells) were observed by double immunostaining. There was no clinicopathological data suggesting
lipoprotein glomerulopathy or
lecithin cholesterol acyltransferase deficiency, both of which are well-known causes of glomerular
lipidosis. The histological findings were relatively similar to those of histiocytic glomerulopathy caused by MAS. As systemic manifestations of MAS, such as
fever,
pancytopenia, coagulation abnormalities,
hyperferritinemia, increased liver
enzyme levels, hepatosplenomegaly, and
lymphadenopathy were minimal, this patient was clinicopathologically diagnosed as having renal-limited MAS. Although optimal treatment strategies for MAS in kidney transplant patients remains unclear, we strengthened
lipid-lowering
therapy using
pemafibrate, without modifying the amount of
immunosuppressants. Serum
triglyceride levels were normalized with this treatment; however, the patient's extensive
proteinuria and renal dysfunction did not improve. Biopsy analysis at 1 year after the
transplantation demonstrated the disappearance of glomerular foamy changes, but the number of glomerular infiltrating cells remained similar.
CONCLUSION: To our knowledge, this is the first reported case of glomerular
lipidosis in a transplanted kidney. Increased interaction-activation of histiocytes (macrophages) and CD8+ T-cells, the key pathogenic feature of MAS, was observed in the glomeruli of this patient, who did not demonstrate overt systemic manifestations, suggesting a pathological condition of renal-limited MAS. The clinical effects of
triglyceride-lowering
therapy were limited, suggesting that
hypertriglyceridemia was not the cause of but rather may be a consequence of renal-limited MAS.