A case report of neonatal alloimmune thrombocytopenic purpura: the importance of correct diagnosis for future pregnancies

Abstract

Context: Neonatal alloimmune thrombocytopenic purpura (NAITP) is a neonatal disorder characterized by maternal alloimmunization against fetal platelet antigens inherited from the father. Intracranial hemorrhage leading to death or permanent neurological disability may occur in the fetus.

Case report: A healthy 30-year-old woman gave birth to her first baby by cesarean after an uneventful 36-week pregnancy. Ten hours after birth, the infant presented severe petechiae, with platelet count of 8 x 10(3)/microl. The mother's platelet count was normal (180 x 10(3)/microl). The infant re ceived intravenous immunoglobulin and was discharged 18 days later, with platelet count of 100 x 10(3)/microl. The cause of thrombocytopenia was not elucidated at that time. One year later, the infant died of neuroblastoma. Since the parents wanted another child, they were referred for investigation of this thrombocytopenia. Platelet genotyping and platelet antibody screening were performed, showing total HPA-1 system mismatch between mother (HPA-1b1b) and father (HPA-1a1a), with anti-HPA-1a antibodies in the mother's serum. We concluded that the first baby was born with NAITP. Thus, in the second pregnancy, the mother was treated with several infusions of intravenous immunoglobulin. Careful ultrasound monitoring was performed, with normal results for mother and fetus throughout the pregnancy. The second baby was born by cesarean at 39 weeks, presenting 92 x 10(3) platelets/microl six hours after birth. The baby's platelets were genotyped as HPA-1a1b and the mother's serum again showed anti-HPA-1a antibodies. No clinical bleeding was observed. Intravenous immunoglobulin therapy was an effective treatment for preventing NAITP in the second baby.

Figure 1. a) Absorbance values obtained by MAIPA technique, testing the mother's serum against a panel of genotyped platelets in a case of neonatal alloimune thrombocytopenic purpura. The mother's serum was strongly reactive against HPA-1a1a and HPA-1a1b donor platelets (bars 4, 5, 6) but was negative against HPA-1b1b donor platelets (bars 2, 3), thus showing presence of anti-HPA-1a alloantibodies. No autoantibodies were detected (bar 1).

Figure 1b). Flow cytometry results. The gray histogram is a positive control; the gray line histogram is a negative control; the positive region is where all the positive histograms must be; the black histogram is the mother's serum against platelets typed HPA-1a1a, showing positive result; the black continuous line (overlapping with negative control) is the mother's serum against platelets typed HPA-1b1b, showing negative result.