A 31-year-old man with no significant past medical history presented to an urgent care center with complaints of fatigue, rash, and epistaxis. Two and a half weeks prior, he received his second scheduled dose of the Pfizer-BioNTech mRNA SARS-CoV-2 vaccine. Within twenty-four hours of vaccine administration, he developed fatigue and a petechial rash across his waistband. Symptoms worsened over the next several weeks, and he noted easy bruising as well as additional petechial lesions. Of note, the patient had received the first scheduled dose of the two-dose live measles, mumps, and rubella (MMR) vaccine series exactly three and six weeks prior to receiving the first and second doses of the Pfizer-BioNTech mRNA SARS-CoV-2 vaccinations, respectively. Complete blood count showed a white cell count of 5.1 x 109/L, hemoglobin 14.8 g/dL, and platelet count of 1,000/microL, and he was subsequently admitted to hospital for additional evaluation and management.
Physical examination was notable for a well-appearing young male with normal vital signs. Skin examination revealed a scattered petechial rash along the right scapular area of the patient's back and across the patient's waistline (Figure 1). The remainder of his exam was unremarkable. Additional laboratory testing showed a normal lactate dehydrogenase of 173 IU/mL, haptoglobin 22 mg/dL, and fibrinogen 233 mg/dL. Testing for HIV and hepatitis C was negative. Vitamin B12 and folate were within the normal range. Review of the peripheral blood smear was notable for markedly reduced platelet count with rare, large circulating platelets. No schistocytes or other distinctive erythrocyte abnormalities were identified (Figure 2). A diagnosis of immune thrombocytopenia purpura (ITP) was made, and the patient was treated with intravenous immune globulin 1 g/kg and glucocorticoids. He was also transfused 2 units of platelets. Platelet count improved significantly to 95,000/microL by hospital day 2, and he was subsequently discharged home. Repeat measurement of his platelet count 3 days after discharge was 472,000/microL. Glucocorticoids were discontinued, and he remained with normal hematologic parameters at 5 weeks after diagnosis.