Isolated massive histiocytes renal interstitial infiltration: a case report of an unexpected cause of acute kidney injury in a kidney transplant recipient

BACKGROUND: Acute kidney injury is a frequent cause of hospital readmission in kidney transplant recipients (KTR), usually associated with infections and graft rejection. Herein, we report a case of an unusual cause of acute kidney injury in a KTR (massive histiocytes renal interstitial infiltration). CASE PRESENTATION: A 40-year-old woman was submitted to a second kidney transplant. One year after surgery, she presented asthenia, myalgia, and fever, haemoglobin 6.1 g/dL; neutrophils: 1.3 × 109/µL; platelets: 143 × 109/µL; blood creatinine 11.8 mg/dL, requiring dialysis. A kidney biopsy revealed diffuse histiocytic infiltration, which was assumed due to dysregulated immunological activation triggered by infections. The patient had multiple infections, including cytomegalovirus infection (CMV), aspergillosis, bacteraemia, and urinary tract infections, which could trigger the immune response. Haemophagocytic lymphohistiocytosis (HLH) was ruled out. The present case highlights the occurrence of isolated massive renal interstitial infiltration of histiocytes that does not meet the criteria for HLH or other related pathologies. CONCLUSIONS: Renal histiocyte activation and infiltration may have been initiated by an immunological mechanism similar to what occurs in HLH and infectious processes. The present case highlights the occurrence of isolated massive renal interstitial infiltration of histiocytes that does not meet the criteria for HLH or other related pathologies.