Plasma Exchange for Thrombotic Microangiopathy Associated With Rectal Cancer Presenting With Acute Kidney Injury: A Case Report.

Thrombotic microangiopathy (TMA) is an acute syndrome characterized by microangiopathic hemolytic anemia, thrombocytopenia, and ischemic end-organ damage resulting from platelet-rich microthrombi obstructing the microvasculature. The kidney is particularly vulnerable to TMA-mediated injury due to its numerous microvessels, often leading to acute kidney injury (AKI). AKI induced by TMA can manifest in oncological conditions, although infrequently. Rectal cancer presenting with TMA-related AKI as the initial manifestation is even rarer, posing a diagnostic challenge for nephrologists. We describe a 62-year-old man admitted with AKI followed by severe thrombocytopenia and anemia. During the diagnostic workup to exclude thrombotic thrombocytopenic purpura, the patient achieved complete hematological recovery after hemodialysis and plasma exchange (PEX), which enabled the performance of a renal biopsy. The underlying etiology was TMA on renal biopsy. However, persistent elevation of lactate dehydrogenase and new‑onset of bone pain prompted further evaluation. The magnetic resonance imaging scan and positron emission tomography-computed tomography subsequently confirmed rectal cancer with bone and liver metastases. This case illustrates that AKI secondary to cancer-related TMA may present as the initial clinical manifestation of an underlying malignancy. Renal biopsy plays a crucial role in establishing a definitive diagnosis and guiding subsequent management. Furthermore, PEX was associated with hematological improvement in this patient, but its overall clinical benefit remains to be determined as the patient remained dialysis‑dependent.