Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT)-like Syndrome: A Case Report and Some Considerations on a Novel Diagnostic and Therapeutic Challenge

<b>Background and Clinical Significance:</b> Disorders caused by platelet-activating antibodies targeting platelet factor 4 (PF4) are recognized as the cause of severe thrombotic events and are not restricted to heparin-induced thrombocytopenia (HIT). <b>Case Presentation:</b> We report a 67-year-old man with thrombocytopenia and extensive portal-splenic-mesenteric vein thrombosis complicated by intestinal ischemia. Despite intravenous unfractionated heparin (UFH), his condition worsened toward pulmonary embolism, septic shock, and multi-organ failure. Thrombolysis with alteplase was also ineffective. Both thrombophilia testing and autoimmune panels were negative, including those for antiphospholipid syndrome. An anti-PF4 immune thrombotic disorder was hypothesized. Therefore, argatroban was initiated instead of UFH therapy and intravenous immune globulin (IVIG) was administered. The platelet count increased and the patient's clinical condition progressively improved. An anti-PF4/heparin assay on a blood sample collected before IVIG was highly positive. Platelet activation assays did not demonstrate an increased activation after the addition of heparin (the Heparin-Induced Platelet Activation [HIPA] assay was negative) though increased activation was observed with the addition of PF4 (the PF4-Induced Platelet Activation [PIPA] assay was positive), thus defining a VITT-like syndrome. <b>Conclusions:</b> This case report highlights the crucial function of having adequate laboratory facilities available to disentangle different anti-PF4 disorders for an accurate definition of a specific diagnosis, such as VITT-like syndrome, thereby allowing for the most appropriate therapeutic management of these complex pathological conditions. The clinical suspicion of an anti-PF4 immune disorder should be considered in cases of severe, otherwise unexplained, thrombotic events associated with thrombocytopenia. Specific tests like HIPA and PIPA are essential for definitive diagnosis.