[From heparin-induced thrombocytopenia to the emergence of VITT like syndromes].

FROM HEPARIN-INDUCED THROMBOCYTOPENIA TO THE EMERGENCE OF VITT LIKE SYNDROMES. Heparin-induced immune-allergic thrombocytopenia (HIT) and vaccine-induced thrombotic immune thrombocytopenia (VITT) first described in 2021, share pathophysiological mechanisms involving anti-PF4 antibodies. HIT results from the formation of anti-PF4/heparin antibodies, leading to thrombocytopenia associated with a hypercoagulable state. VITT, which occurs following adenoviral vector vaccination, exhibits similarities with HIT but arises without prior heparin exposure and often involves anti-PF4 antibody reactivity that is independent of heparin. The diagnosis of both HIT and VITT relies on specific biological tests conducted in expert centers to confirm the pathogenicity of anti-PF4 antibodies. Since 2022, the discovery of a new acquired autoimmune thrombotic disease, referred to as "VITT-like", has been reported in infectious or hematological contexts, further expanding the spectrum of immune-thrombotic disorders associated with anti-PF4 antibodies.