PO132 | POST KIDNEY TRANSPLANT PRESENTATION OF ACQUIRED THROMBOTIC THROMBOCYTOPENIC PURPURA: A CASE OF PRE-EXISTING ADAMTS13 INHIBITORS

G. Murante^1|2|5, S. Bergonzi^1|2|5, M. Capetta^1|2|5, F. Valeri^1|2, C. Dainese^1|2, A. Valpreda⁴, R. Pastorino^1|5, F. Bocchi^1|5, L. Biancone³, E. Gallo³, B. Bruno^2|5, A. Borchiellini^1|2 | ¹Regional Centre for Hemorrhagic and Thrombotic Diseases; ²Division of Hematology; ³Nephrology Dialysis and Transplant U; ⁴Central Lab. Baldi and Riberi, AOU Città della Salute e della Scienza di Torino, Italy; ⁵Dep. of Molecular Biotechnology and Health Sciences, University of Turin, Italy

Background and aims. Acquired thrombotic thrombocytopenic purpura (aTTP), otherwise known as Moschcowitz syndrome, is a subtype of thrombotic microangiopathy characterized by the simultaneous presence of microangiopathic hemolytic anemia, thrombocytopenia and multiorgan ischemic damage. The pathogenetic mechanism underlying the above-mentioned triad lies in the unsuccessful degradation of the high molecular weight multimers of von Willebrand factor (vWF), secreted by the endothelial cells, because of a deficiency in ADAMTS13, a metalloproteasis aiming to prevent an excessive linkage and consumption of platelets when adherent to subendothelium through the vWF. The pathogenetic mechanism of the acquired ADAMTS13 deficiency is predominantly autoimmune, because of the presence of circulating antibodies of the IgG family directed against the cysteine-rich spacer cathalytic domain of the metalloproteasis. Acquired thrombotic thrombocytopenic purpura (aTTP) is a rare but critical complication after kidney transplantation. Its diagnosis is often masked by post-operative complications or drug-induced microangiopathic hemolytic anemia (TMA), requiring high clinical suspicion for timely intervention. The aim of this abstract is to report a rare case of early-onset post-transplant aTTP in a patient with no prior hematological history, highlighting the diagnostic process and the effectiveness of a multimodal therapeutic strategy including Caplacizumab.
Case report. A 56-year-old Caucasian woman with end-stage renal disease of unknown etiology underwent deceased-donor kidney transplantation in August 2025. The patient's medical history was unremarkable for any known autoimmune or hematological disorders. Standard immunosuppression was initiated with steroids, mycophenolate mofetil, tacrolimus, and anti-thymocyte globulin (ATG). Despite an initially stable nephrological course, the patient developed severe thrombocytopenia (18,000/mmc) and a drop in hemoglobin (10.1 g/dL) on post-operative day (POD). Laboratory findings on POD 6 revealed TMA picture: hemoglobin 7.5g/dL, Platelets 18.000/mmc, schistocytes 1.6%, elevated LDH (709 U/L), indirect bilirubin 2.3 mg/dL and undetectable haptoglobin (<0.3 g/L), with a negative direct Coombs test. Coagulation profiles and graft function (creatinine 0.99 mg/dL) remained stable. With a PLASMIC score of 5 (intermediate risk), ADAMTS13 testing was performed. Results confirmed aTTP, showing ADAMTS13 activity <0.01 U/mL and an inhibitor titer of 19.34 BU. Treatment commenced with daily plasma exchange (PEX) and Rituximab (RTX, 375 mg/sqm), alongside adjusted baseline immunosuppression to mitigate infectious risk. Due to post-operative haemorrhagic risk, Caplacizumab was started after 24 hours. Retrospective analysis of pre-transplant serum revealed positive ADAMTS13 inhibitors (20 BU). Clinical remission was achieved within 5 days, leading to PEX discontinuation. Following rapid ADAMTS13 recovery (0.71 UI/m) and inhibitor clearance, the final RTX dose was omitted. Caplacizumab was ceased after 30 days. The patient was discharged in full clinical and serological remission on POD 30 with stable graft function.
Conclusions. This case highlights the diagnostic challenge of post-transplant aTTP and the critical importance of early ADAMTS13 assessment. The retrospective finding of pre-existing inhibitors suggests that the surgical stress or induction therapy may have triggered the clinical manifestation of a previously silent autoimmune state.