Case Report: Late-onset BK polyomavirus-associated nephropathy with encephalitis, antibody-mediated rejection, and atypical hemolytic uremic syndrome: a rare overlap causing allograft dysfunction, therapeutic challenges, and multidisciplinary management.

BACKGROUND: Kidney transplantation is the definitive treatment for end-stage renal disease. Late allograft dysfunction has complex and heterogeneous etiologies, and concurrent overlapping pathologies pose substantial clinical challenges that require integrated multidisciplinary management.

CASE PRESENTATION: A 23-year-old female with previously stable allograft function on maintenance immunosuppression presented with progressive clinical deterioration 6 years after deceased-donor kidney transplantation. Initial respiratory symptoms progressed to tonic-clonic seizure, neuropsychiatric disturbances and acute renal function decline. She was diagnosed with active BK polyomavirus viremia with encephalitis, complement-mediated atypical hemolytic uremic syndrome (aHUS), and biopsy-proven BK polyomavirus-associated nephropathy (BKPyVAN) plus concurrent C4d-positive antibody-mediated rejection (AMR). A multidisciplinary team delivered an individualized regimen to resolve the therapeutic conflict: 5 plasma exchange sessions, conversion from mycophenolate mofetil to mizoribine to balance viral control and rejection prophylaxis, plus adjunctive symptomatic therapies. Neuropsychiatric symptoms resolved gradually, and hematological parameters and renal function stabilized by day 29 of admission, leading to a stable discharge. However, the patient progressed to allograft failure and required maintenance dialysis at 1-year follow-up.

CONCLUSIONS: This case highlights the complexity of late allograft complications with overlapping pathologies. Timely multidisciplinary consultation and balanced individualized strategies are critical to optimize clinical outcomes in such rare cases.