We have established that our newborn baby with an intracranial haemorrhage has a low platelet count and have debated the likely cause for this. The list of differentials include:
- Maternal ITP (Immune thrombocytopenic purpura: autoimmune destruction of platelets) which can briefly affect the neonate because the antibodies cross the placenta. The baby’s platelet count is usually >20 and can drop lower around day 4 of life. It is rare for significant bleeding to occur in this scenario despite a low platelet count.
- Congenital Infections (TORCH)
- Congenital bone marrow disorders such as Congenital amegakaryocytic thrombocytopenia and Thrombocytopenia with absent radii.
- Acquired disorders – sepsis/DIC being the most common.
- Bernard Soulier Syndrome, or other rare platelet disorders such as MYH9 disorders.
- NAIT Neonatal Allo-Immune Thrombocytopenia.
The above list is by no means exhaustive. For an excellent review of the causes of thrombocytopenia in neonates we would recommend the following review:
Chakravorty, S. and Roberts, I. (2012), How I manage neonatal thrombocytopenia. British Journal of Haematology, 156: 155–162. doi:10.1111/j.1365-2141.2011.08892.x
More on NAIT
- NAIT is a similar process to Haemolytic Disease of the newborn, but involving platelets rather than red cells. Mum is sensitised to an antigen on the fetus’ platelets (which she doesn’t have). She makes antibodies to this antigen and these antibodies cross the placenta, destroying the fetus’ platelets.
- This most frequently happens when baby expresses HPA-1a (Human platelet antigen) and mum doesn’t. Most of the population is HPA-1a positive (98%) and thus only 2% of women and their children could be affected.
- Although most cases of NAIT are due to anti-HPA-1a, but a small number are caused by HPA-5b or other antibodies.
- It should be noted that no antibody is established in 80% of cases of NAIT (which then becomes a diagnosis based on acute, severe thrombocytopenia in an otherwise healthy neonate which resolves spontaneously within 3-4 weeks of birth). These cases are still thought to be antibody mediated, but demonstration of the antibody/identification of the antigen is very difficult and will not alter management in the vast majority of patients.
- Anti-platelet antibodies are detected by MAIPA (monoclonal antibody-specific immobilisation of platelet antigen assay) which is an advanced, complex investigation performed by reference laboratories (in the England this is done by NHSBT). In addition samples taken from both parents are tested to identify the platelet antigens that are expressed by Dad and not Mum – and may therefore be implicated in the process.
- Haemolytic disease of the newborn is rare in first pregnancies, but NAIT is not – between 20-50% of cases occur in a first pregnancy, so there will be no history to guide you. If it has occurred in the first pregnancy it will recur in subsequent pregnancies and tends to be more severe with each pregnancy, i.e the risk of significant bleeding increases.
- 20% of bleeds occur in utero – so the damage may already be done by the time baby is born. Intracranial haemorrhage is the most severe bleeding event and can occur from 20 weeks.
- NAIT is the most common cause of SEVERE thrombocytopenia in a neonate (excluding sepsis). It is more likely to be associated with bleeding than many other causes of thrombocytopenia in this period.
So…We have decided, based on the fact our neonate (who has an intracranial haemorrhage) is term, not septic, has no obvious dysmorphology, has not been exposed to drugs in utero and has a healthy mum (who received appropriate antenatal care) that this baby has NAIT. We’ve sent blood samples for antibody identification (MAIPA) and HPA identification (on mum and dad).
What is our management now? How urgently will you organise your intervention (if any)?
Extra points are available for telling the team about issues that apply specifically to the mother in this case…
Answers on the hashtag #teamhaem – see you over on Twitter!
Cases are, as ever, fictional. We are, as ever, endeavouring to promote learning and are not in a position of authority. We do work hard to bring you high quality cases and discussion and value your participation. Let us know what we do well and any ideas you have for improving this project, topics to cover or any other thoughts. Happy #FOAMed to you all!