[Recent topics in the pathophysiology and treatment of immune thrombocytopenic purpura].

Increased and impaired platelet productions via immunological abnormalities are the main pathophysiological mechanisms of primary immune thrombocytopenia (ITP). Recent studies have revealed that platelet removal from circulation involves not only Fc receptor-mediated phagocytosis of immunoglobulin G autoantibodies-bound platelets but also complement-dependent mechanism and platelet glycoprotein desialylation. Understanding the molecular mechanism of ITP pathophysiology has helped develop many novel molecular targeted drugs, and recent clinical trials have shown their effectiveness. In particular, fostamatinib, which is a Syk inhibitor, inhibits macrophage and B-cell activity and is already been approved in Europe for multidrug-resistant ITP. Recently, coronavirus disease-2019 (COVID-19) vaccine-associated newly-onset or ITP exacerbation has come to attention. Whether COVID-19 vaccines induce de novo ITP remains controversial. However, close attention is necessary after COVID-19 vaccination because a certain number of patients with ITP presented exacerbation after COVID-19 vaccination.

[Acquired hemophilia A following BNT162b2 mRNA COVID-19 vaccination].

Acquired hemophilia A (AHA) is a rare disease characteized by bleeding symptoms caused by decreased factor VIII activity due to the appearance of inhibitors to factor VIII triggered by malignancy or collagen disease. An 86-year-old woman developed purpura on her extremities after the first dose of the BNT162b2 mRNA COVID-19 vaccine. This symptom subsided after a few days. After the second dose of the BNT162b2 mRNA COVID-19 vaccine, purpura appeared again, and the patient was referred to our hospital Her APTT was remarkably prolonged to 110 seconds, and a cross-mixing test revealed an inhibitor pattern. Since FVIII activity was <1% and FVIII inhibitor was 51.6 BU, she was diagnosed with AHA. Prednisolone therapy was started, and coagulative complete remission was achieved. Because acquired hemophilia can develop after mRNA COVID-19 vaccination, as in this case, it is critical to monitor the appearance of bleeding symptom.