Neonatal alloimmune thrombocytopenic purpura

Thrombocytopenia in Neonates

Thrombocytopenia defined as platelet count below 150,000/μL is not an uncommon event at the neonatal intensive care unit (NICU). In our region we calculated a prevalence of nearly 2 of 1000 live births. Early-onset neonatal thrombocytopenia (NT) occurring within the first 72 hours of life is more common than late-onset NT. Preterm infants are affected more often than term infants and bacterial infection is the most common diagnosis associated with NT. There are a lot of maternal, perinatal, and neonatal causes associated with NT and complications include bleedings with potentially life-threatening intracranial hemorrhage. Alloimmune thrombocytopenia (NAIT) often presents with severe thrombocytopenia (<30,000/μL) in otherwise healthy newborns and needs careful evaluation regarding HPA-1a antigen status and HLA typing. Platelet transfusions are needed in severe NT and threshold platelet counts might be at ≤25,000/μL irrespective of bleeding or not. Immune mediated NT recovers within 2 weeks with a good prognosis when there happened no intracranial hemorrhage. This short review gives an overview on etiology and causes of NT and recommendations regarding platelet transfusions.

Neonatal thrombocytopenia-causes and outcomes following platelet transfusions

We evaluated the causes for neonatal thrombocytopenia (NT), the duration of NT, and the indications of platelet transfusions (PT) by means of a retrospective cohort study over a 23-year period. Neonates with NT were identified via ICD-10 code D69.6. Of 371 neonates (1.8/1000 live births) with NT, the majority (312; 84.1%) had early onset thrombocytopenia, and 282 (76%) were preterm born. The most frequent causes for NT were early and late onset sepsis and asphyxia. The mean duration of thrombocytopenia was 10.2 days and was negatively correlated (KK = - 0.35) with the number of PT. PT were given to 78 (21%) neonates, 38 (49%) of whom had very severe NT. The duration of NT was positively related to the severity of NT and the number of subsequent PT. A mortality rate of 10.8% was significantly associated with bleeding signs (p < 0.05) and correlated with increasing number of PT (p < 0.05) but not with the severity of NT (p = 0.4). In the case of relevant hemorrhage, PT did not influence the mortality rate (p = 0.09). All deaths followed neonatal sepsis.

CONCLUSIONS

Prematurity and diagnoses including early and late onset sepsis and asphyxia were the most common causes of NT. Mortality was not associated with the severity of NT but increased with the number of PT. What is Known: • The causes for neonatal thrombocytopenia (NT) are well known. • The effects of platelet transfusions (PT) and its indications are still a matter of debate and recommendations differ widely. What is New: • The duration of NT is positively related to the severity of NT and the number of subsequent PT. • The mortality rate is not associated with the severity of NT but increases with increasing numbers of PT and in the case of relevant intraventricular hemorrhage (≥ grade II), PT does not influence the mortality rate.

The HLA system: genetics, immunology, clinical testing, and clinical implications

The human major histocompatibility complex HLA is located on the short arm of chromosome 6. It is known to be the most polymorphic genetic system in humans. The biological role of the HLA class I and class II molecules is to present processed peptide antigens. The HLA system is clinically important as transplantation antigens. Molecular HLA allele typing is routinely performed to provide HLA class I and class II allele matching in unrelated donor hematopoietic stem cell transplantation. Prospective lymphocyte crossmatching is critical in solid organ transplantation to prevent allograft rejection. HLA alloimmunization causes various problems in transfusion therapy. The HLA system is associated with certain diseases, but its underlying mechanisms are not yet fully explained.

Prenatal intracranial hemorrhage and neurologic complications in alloimmune thrombocytopenia

Neonatal alloimmune thrombocytopenia results from platelet-antigen incompatibility between mother and fetus, leading to antibody-mediated destruction of fetal platelets. With a prevalence of 1 in 1000 births, approximately 4000 infants born in the United States each year develop neonatal alloimmune thrombocytopenia. Ten to 20% of affected neonates develop intracranial hemorrhage, with 25 to 50% occurring prenatally. We report three infants who developed prenatal hemorrhage. One died in utero, and the other two had cerebral porencephaly and neurologic deficits. Infants with neonatal alloimmune thrombocytopenia have elevated risks of perinatal death and neurologic complications, including cerebral palsy, hypotonia, cortical blindness, developmental delay, seizures, and psychomotor retardation. We also report our retrospective review of the New England Medical Center neonatal intensive care unit between 1990 and 1999. Using current management guidelines, including treatment of the mother with a weekly infusion of high-dose (1-2 g/kg) intravenous immunoglobulin and/or corticosteroids, all eight infants with neonatal alloimmune thrombocytopenia did well.

Neonatal alloimmune thrombocytopenia due to anti-Nak(a)

BACKGROUND

The accurate diagnosis of neonatal alloimmune thrombocytopenia is essential in the effective treatment of potentially serious bleeding in neonates.

CASE REPORT

Reported here is a case of a full-term female baby who was delivered by vacuum extraction from a gravida 1 para 1 healthy mother. She presented with generalized petechiae and bilateral cephalhematoma, which she had had since birth. At 7 hours of life, she had an upper gastrointestinal hemorrhage and was found to have severe anemia and marked thrombo-cytopenia. Coagulation screening tests were normal. The diagnosis of neonatal alloimmune thrombocytopenia was suspected, and maternal serum was collected for further study. The baby was treated with a single dose of hydrocortisone (10 mg/kg) and IVIG (400 mg/kg) while waiting for irradiated platelets from her mother. After 30 mL of a transfusion of maternal platelets, the baby's platelet count rose dramatically, from 15,000 to 162,000 per microL, and it remained stable at that level. She was discharged on the 10th hospital day in good condition. During the follow-up period of 8 months, her growth and development were satisfactorily normal, as well as her platelet count. A high-titered platelet antibody was detected in the maternal serum by use of a solid phase platelet adherence technique.

RESULTS

The specificity of the platelet antibody was identified as anti-Nak(a) by the mixed passive hemagglutination test method.

CONCLUSION

These findings suggested a diagnosis of NAIT caused by anti-Nak(a).

Feto-maternal alloimmune thrombocytopenia: a literature review and statistical analysis

Exploring prognostic factors that determine outcomes in fetomaternal alloimmune thrombocytopenia (FMAIT), a search of Medline was performed covering the years 1966 to April 1998. 376 articles were collected and reviewed; 140 articles contained the case histories of 297 mothers and 433 pregnancies that fulfilled entry criteria. More than 30 data variables were sought from these cases. The data were analysed using SPSS and Arcus Quickstat Biomedical. Nineteen different antigen incompatibilities were documented, the majority being human platelet antigen (HPA)-1a (77.3%), HPA-3a (3.5%) and HPA-5b (3.5%). The relative risk reduction (RRR) in mortality with any intervention was 57% (0.19-0.77) p = 0.009. Treatment of HPA-1a (PlA1) pregnancies with intravenous immunoglobulin (IVIG) increased the likelihood of a neurologically normal outcome, relative risk (RR) 1.68, confidence interval (1.3-2.2) p = 0.0003. Treatment of HPA-1a (PlA1) pregnancies with only antenatal complementary platelet transfusions increased the likelihood of a neurologically normal outcome, RR 1.63 (1.1-2.1) p = 0.01. Despite reviews of more than 400 cases of FMAIT, few prognostic variables are identifiable. Although IVIG appears to reduce the risk of intracranial haemorrhage (ICH), the dosage and timing of IVIG treatment was varied. This study highlights the need for standardised and directed research.

The management of alloimmune neonatal thrombocytopenia

Neonatal alloimmune thrombocytopenia (NAITP), defined as thrombocytopenia (platelet count < 150 x 10(9)/l) due to transplacentally acquired maternal platelet alloantibodies, occurs in approximately 1 per 1200 live births in a Caucasian population. In such a population, the majority (> 75 percent) of cases are due to fetomaternal incompatibility for the platelet specific alloantigen, HPA-1a (P1A1, Zwa). Incompatibility for the HPA-5b (Bra) alloantigen is the next most frequent cause of NAITP in Caucasians; much less common is NAITP due to incompatibility for HLA, blood group ABO or other platelet-specific antigens. In non-Caucasian populations (e.g. Orientals) HPA-1a incompatibility is a rare cause of NAITP and other alloantigens e.g. HPA-4b (Penb, Yuka) are implicated. The greatest clinical challenge relates to the antenatal management of pregnant women alloimmunized to the HPA-1a (P1A1, Zwa) antigen, and particularly the subset of such women who have a history of a previously affected infant with severe thrombocytopenia and/or intracranial hemorrhage (ICH). The risk of antenatal ICH in the fetus of such women is high enough to merit intervention, either weekly infusion of high-dose intravenous immunoglobulin G (IVIG) with or without corticosteroids given to the mother (the preferred approach in North American centres), or repeated in-utero fetal platelet transfusions (the preferred treatment approach in some European centres). Post-natal management of severely affected infants centres on the rapid provision of compatible antigen-negative platelets harvested from the mother or a phenotyped donor. The value of antenatal screening programs to detect 'at risk' alloimmunized women during pregnancy continues to be debated.

Platelet and neutrophil alloantigen genotyping in clinical practice

Immune responses to platelet and neutrophil alloantigens are involved in the pathogenesis of several clinical syndromes including: neonatal alloimmune thrombocytopenia (NATP), post-transfusion purpura (PTP), refractory responses to platelet transfusion, neonatal alloimmune neutropenia (NAN), transfusion-related acute lung injury (TRALI), and chronic benign autoimmune neutropenia of infancy. Initially, platelet alloantigens were only characterized serologically. Subsequently, they were localized to specific platelet surface glycoprotein structures and ultimately defined to the level of nucleic acid polymorphisms on platelet glycoprotein genes. These advances allowed the tools of molecular biology to be applied to typing for platelet alloantigens. The advantages of such typing methods include: 1) patient platelets are no longer required for the typing assays, and therefore, platelet types can be established on extremely thrombocytopenic samples (by using peripheral blood white blood cells [WBC]); 2) The genotyping methods eliminate the requirement for rare serologic reagents. A number of different genotyping methods have been developed. These include: restriction fragment length polymorphism (RFLP), sequence specific primers (SSP), and Dot-Blot hybridization. Clinical applications of this methodology include: determining the platelet genotype of fetuses at risk for NATP, in the diagnosis of PTP, and identifying causes of refractory responses to platelet transfusions. Analogous to platelet alloantigens, a limited number of neutrophil alloantigens can now be determined by molecular biologic methods. The new methods obviate the need to isolate fresh neutrophils for serologic typing and do not require rare serologic reagents. To date, molecular polymorphisms associated with alloantigens on the neutrophil Fc gamma RIIIb surface glycoprotein have been elucidated. These include the allo-antigens NA1, NA2, and SH.

Purpura in infants and children

Hemorrhage into the skin (purpura) may result from abnormalities in any of the three components of hemostasis: platelets, plasma coagulation factors, and blood vessels. The morphology, size, and distribution of the hemorrhagic lesions are helpful diagnostic features. The main causes of purpura in the newborn and the more common hemorrhagic disorders in children are reviewed.

Platelet and hemorrhagic disorders associated with pregnancy: a review. Part I

Disorders of coagulation remain an important potential cause of maternal morbidity and mortality. Bleeding disorders in pregnancy, unlike disorders of hypercoagulability, most often can have little impact on the mother but devastating consequences for the fetus. Further complicating the issue is that not all disorders of coagulation are inherited. Some are due to maternal illnesses unique to pregnancy, others are due to drug ingestion, and yet others remain idiopathic. In still other instances, thrombocytopenia is a minor consequence of a more severe disorder and will resolve when the inciting agent is removed or treated. A basic understanding of the pathophysiology of various conditions that lead to bleeding diathesis in pregnancy is necessary in order to effectively manage these varied clinical disorders. In addition, knowledge of whether the major morbidity is fetal or maternal or both can impact management. This review is concerned with the etiology, pathophysiology, diagnosis, and general management of commonly encountered disorders in pregnancy that place the mother and fetus at increased morbidity and mortality because of the potential for hemorrhage. Acutely acquired disorders and the resultant maternal manifestation versus a chronic disease process that is altered by the state of pregnancy are distinguished. Where possible, the incidence and prognosis of the disorder are provided. Actual cases are included to illustrate how similar presentations of distinctly different disorders can confuse and complicate an accurate diagnosis that is essential for appropriate management.

Thrombocytopenia in the neonate

Pediatricians caring for newborns will eventually be confronted with the problem of thrombocytopenia in the neonatal period. Familiarity with the differential diagnosis of neonatal thrombocytopenia and understanding the pathogenesis of the more common entities allows physicians to design a selective diagnostic and therapeutic plan to benefit these thrombocytopenic infants.

Neonatal thrombocytopenia caused by passive transfer of anti-PLA1 antibody by blood transfusion

A premature male infant with hyaline membrane disease received a 34 ml transfusion of packed erythrocytes from a CPDA1 blood unit on day 2 with no adverse consequences. On day 34 he was given a transfusion, and the platelet count decreased. Intravenous immune globulin therapy was initiated and the platelet count steadily increased. Human leukocyte (HLA) antigen and platelet antibody testing showed that the thrombocytopenia was due to passive transfer of platelet-specific antibody from the blood donor.

The prenatal identification of fetal compatibility in neonatal alloimmune thrombocytopenia using amniotic fluid and variable number of tandem repeat (VNTR) analysis

Most severe episodes of neonatal alloimmune thrombocytopenic purpura (NATP) are caused by antiplatelet alloantibodies against the HPA-1a (PlA1) antigen. However, half of subsequent fetuses produced from a HPA-1a/b father (genotypic frequency 28%) will result in a child who is not affected. Some investigators manage NATP by confirming the fetal platelet phenotype using percutaneous umbilical cord sampling, a procedure that carries a low but real risk of fetal morbidity and mortality. More recently, physicians determine the fetal platelet antigen genotype using DNA derived from amniotic fluid or chorionic villus samples. All therapy is withdrawn for a fetus who genotypes as HPA-1b/b. However, since the fetus is the same genotype as the mother, there can be uncertainty about the origin of the genetic material and thus the validity of the fetal genotype. The inappropriate withdrawal of therapy for a erroneously genotyped fetus could be fatal, and consequently many physicians advocate fetal HPA-1 phenotyping with confirmation using percutaneous umbilical blood sampling. In this report we describe the management of two pregnancies with previously affected infants due to anti-HPA-1a alloantibodies. Both husbands were HPA-1a/b. For the current pregnancies, amniotic fluid was collected at 20 or 29 weeks of gestation, and the platelet genotype indicated that the fetuses were HPA-1b/b. The fetal origin of the amniotic fluid derived DNA was confirmed by the forensic technique of DNA profiling using variable number of tandem repeat (VNTR) analysis. All therapy was withdrawn, percutaneous umbilical blood sampling was not performed, and both women vaginally delivered healthy non-thrombocytopenic infants. The application of platelet alloantigen genotyping using DNA from amniotic fluid cells identified the HPA-1b/b fetus, and VNTR analysis confirmed that the tissue was fetal derived, thus avoiding the necessity for percutaneous umbilical blood sampling. The use of this approach in patients at risk will avoid additional investigation and treatment in approximately one-seventh of all NATP pregnancies involving the HPA-1a antigen.

Nature of the brain lesion in fetal allo-immune thrombocytopenia

Study of three fetuses with allo-immune thrombocytopenia, one with autopsy findings, and comparison with existing data have permitted speculation on the nature of the initial lesion within the brain. The commonest first bleeding site is probably underneath the molecular layer of the cerebral cortex, often within the temporal lobe. Small haemorrhages may appear to be (sub)pial, but expansion will lead to so-called subarachnoid haematoma. Communication with the adjacent lateral ventricle will contribute to post-haemorrhagic hydrocephalus. Occasionally, the initial haemorrhage is within the ventricle; such a pattern may lead to post-haemorrhagic hydrocephalus, often with a porencephalic component. In utero follow-up of fetuses at risk for allo-immune thrombocytopenia will have to focus on superficial cerebral haemorrhage for early detection of brain involvement.

Fetal and neonatal thrombocytopenia

Thrombocytopenia is defined as platelet count less than 150,000 plat/mm3. Etiologic factors involved include immunological (NAIT and ITP), fetal infectious disease, chromosomal and nonchromosomal, and miscellaneous causes. While the understanding of fetal thrombocytopenia is driven by reason to do fetal blood sampling, discovery of neonatal thrombocytopenia is driven by blood counts performed because of the risk of infections. The most serious consequence of thrombocytopenia in the fetus/neonate is intracranial hemorrhage which can occur in utero as early as 18 weeks gestation. The key factor in perinatal prevention of intracranial hemorrhage is early diagnosis and treatment, possibly in utero. Cordocentesis under direct ultrasound guidance and platelet transfusions have played a major role in the management of fetal/neonatal thrombocytopenia. Ongoing studies and high resolution ultrasound will continue to explore and hopefully clarify fetal and neonatal thrombocytopenia and facilitate recognition of primary and secondary thrombocytopenias.

Anti-Bak(a) neonatal alloimmune thrombocytopenia: possible prevention by intravenous immunoglobulin

Neonatal alloimmune thrombocytopenia (NAIT) most commonly involves antibodies directed against the PlA1 antigen, but other platelet specific alloantigens have been associated with it. We describe the case of a mother whose first three infants developed NAIT secondary to anti-Bak(a) antibodies, while her fourth infant did not. The three affected infants were treated postnatally with platelet transfusions. The fourth infant was treated antenatally with one dose of intravenous immunoglobulin (IVIg) given to the mother. Postpartum analysis revealed the infant's platelets to be Bak(a)-positive but negative for elevated IgG. Maternal serum reacted with neonatal platelets in vitro, but cord serum was negative for antiplatelet antibodies. These clinical observations do not prove the efficacy of IVIg; however, they raise several questions: Why wasn't this infant thrombocytopenic? Why didn't the umbilical cord contain maternal antibody? Was the single dose of IVIg responsible for preventing NAIT? IVIg is currently under investigation in a clinical trial evaluating its effectiveness in preventing NAIT in mothers with anti-PlA1 antibodies, where it has shown some success. There have been no reports of the use against anti-Bak(a) antibodies. We suggest that a weekly dose schedule may not be necessary for all affected pregnancies, and antibodies with specificity other than anti-PlA1 may require less vigorous therapy.

Neonatal alloimmune thrombocytopenia. A case report and a review of the literature

A 32-year-old woman in her third pregnancy underwent fetal blood sampling because of a previous child with neonatal thrombocytopenia. At 33 weeks' gestation, fetal thrombocytopenia was diagnosed. Treatment was instituted antenatally with serial fetal platelet transfusions and corticosteroid therapy. Delivery was by Caesarean section at 37 weeks' gestation. Neonatal treatment included further platelet transfusion and immunoglobulin infusion. Recovery of the neonate was complete on discharge from hospital 10 days after birth. The aetiology, diagnosis, clinical presentations and therapeutic options in cases of alloimmune thrombocytopenia are discussed.

A rapid and sensitive immunoassay for antibodies against alloantigens on human platelet glycoproteins (BIPA)

A rapid and sensitive enzyme immunoassay has been developed for the detection and specification of alloantibodies against human platelet antigens (HPA) on platelet membrane glycoproteins. Human platelet glycoprotein complexes were coupled by monoclonal antibodies to immunomagnetic beads with sheep anti-mouse IgG directed antibodies. These beads served as solid-phase target antigens for human alloantibodies in a modified MAIPA assay. This test provided high sensitivity, permitting the identification of antibodies against membrane receptors and required only 1 h of assay time. The specificity and sensitivity of this assay were evaluated in serum samples from polytransfused patients and compared with standard immunoassays employing antigen coated immunowells.

Prenatal recognition of central nervous system complications of alloimmune thrombocytopenia

The radiological findings associated with alloimmune thrombocytopenia have not been well described. We present two such cases diagnosed in utero by ultrasound and discuss the radiographic findings of intracranial hemorrhage and hydrocephalus secondary to alloimmune thrombocytopenia. An awareness of this entity and its early diagnosis and intervention may greatly reduce the morbidity and mortality associated with alloimmune thrombocytopenia.

Management of fetal alloimmune thrombocytopenia by weekly in utero platelet transfusions

Alloimmune neonatal thrombocytopenia (ANT) may cause intracranial haemorrhage in utero as well as at delivery. Recent management has concentrated on attempts to minimise fetal thrombocytopenia and prevent its complications. This report describes further experience with the use of repeated intravascular transfusions of compatible platelets in utero. The patient studied had already had one infant with intracranial haemorrhage due to ANT. In her next pregnancy, weekly intra-uterine platelet transfusions were given from 26 weeks, but intra-uterine death occurred at 30 weeks after the mother had a heavy fall. In her most recent pregnancy, weekly intravascular transfusions of platelets were given by cordocentesis from 29 to 34 weeks. The fetal platelet count was maintained above 30 X 10(9)/l for almost all of the last 6 weeks of pregnancy before delivery of a normal infant by Caesarean section at 35 weeks' gestation. This approach is effective in preventing severe fetal thrombocytopenia in the last trimester of pregnancy and is contrasted with alternative treatments of ANT. Further data are required to determine the efficacy and risks of these treatments.

Prenatal diagnosis of platelet disorders

The antenatal diagnosis of platelet disorders represents real progress in the early detection of haemorrhagic diseases occurring in the fetus. However, the diagnosis is only possible in some cases during the first trimester of gestation, and not in the first weeks as is the case for other hereditary disorders such as abnormal haemoglobins. This delay can be reduced now that the molecular abnormalities responsible for some platelet disorders have been discovered. If the region of chromosome 17 and the DNA sequence coding for the glycoproteins GP IIb-IIIa were known, this would make possible the recognition of the gene defect responsible for Glanzmann's thrombasthenia. This could also permit the diagnosis of Glanzmann's thrombasthenia at the gene level, i.e. during the first weeks of gestation. However, the use of gene markers could be limited by the fact that a monomorphic clinical expression of Glanzmann's thrombasthenia could correspond to different genetic mutations which can all result in a defect in GP IIb-IIIa synthesis and assembly. If such diagnosis could be made very early, it would only represent real progress if a specific treatment could be applied. New therapeutic approaches to immune thrombocytopenia during pregnancy appear to be possible and can be applied when there is a risk to the fetus, they are still either experimental or anecdotal and there is a real need for a well-designed clinical trial. In all fetal platelet disorders, the risk of fetal death following fetal blood sampling must not be underestimated and very careful, intensive care is necessary after such an investigation. In the absence of a specific therapy, this antenatal diagnosis must be restricted to cases in which the risk of severe haemorrhagic complications are anticipated and where there is a well-documented family history. The patients must be properly informed of all the aspects of the investigation, including the possible risks. As has been the case for other haematological disorders, progress will be made, and we can anticipate that eventually in utero bone-marrow transplantation or gene correction be performed to cure the disease before birth.

Management of alloimmune neonatal and antenatal thrombocytopenia

Neonatal and antenatal alloimmune thrombocytopenia is induced by maternal antibodies against platelet-specific fetal antigens. This disease is rare but potentially severe because of intracranial bleedings which may occur during pregnancy or around birth. In the last decade our knowledge of this disorder has markedly advanced. New techniques are used in platelet immunology. New platelet antigens involved in these perinatal thrombocytopenias have recently been discovered. A group of women likely to produce the responsible platelet antibodies has been genetically defined as regards the PLA1 antigen. The quality of the sonographies and the possibility of performing cord vein puncture in early pregnancy afford a new approach in the management of perinatal alloimmune thrombocytopenias. But more must be done to prevent the complications of this disease.