[Immune thrombocytopenia after BNT162b2 mRNA COVID-19 vaccination].

A 95-year-old male developed general subcutaneous petechiae, tongue hematoma, and melena two days after receiving the second BNT162b2 mRNA COVID-19 vaccine. Two days later, his platelet count decreased to below 1,000/µl. Laboratory testing was positive for a slight increase in D-dimer, Helicobacter pylori (H. pylori) immunoglobulin G (IgG) antibody, lupus anticoagulant, and anticardiolipin IgG antibody levels. There were no severe infections or symptomatic thrombosis. Platelet transfusions were transiently effective. He was diagnosed with newly developed immune thrombocytopenia (ITP). We administered prednisolone (PSL) at 0.5 mg/kg/day and intravenous immunoglobulin (IVIG) at 0.4 g/kg/day. From the following day, his platelet count rapidly increased, with an improvement in bleeding tendency. H. pylori was eradicated after platelet count recovery. Thrombocytopenia did not relapse although PSL was tapered three months later. Causes of thrombocytopenia after SARS-CoV-2 vaccination include ITP, vaccine-induced immune thrombotic thrombocytopenia, and thrombotic thrombocytopenic purpura. Differential diagnosis is important to determine the proper therapy. Case reports of newly diagnosed ITP after SARS-CoV-2 vaccination have been increasing recently. In these cases, including ours, the responses to steroids and IVIG were good. Further follow-up studies are needed to manage thrombocytopenia following SARS-CoV-2 vaccination.