Acute immune thrombocytopenia purpura
Purpura arising secondary to a fall in platelet count thought to be of immune origin.
Commonest cause of thrombocytopenia.
More common in childhood, peak onset 2–10 years.
M = F
The cause is largely not understood but it may arise 1–4 weeks after a viral infection. Platelet associated IgG antibodies are detectable in the serum of patients.
The autoantibody binds to circulating platelets, which are then removed in the spleen. Clinical problems only become apparent when the platelet count falls below 50 × 109 per litre.
Children present with petechiae and superficial bruising, however in severe cases mucosal bleeds occur such as epistaxis and menorrhagia. Cerebral haemorrhages are rare. There may be a history of a viral illness in the previous four weeks.
Full blood count shows the level of platelets. Bone marrow aspiration can be used to confirm the diagnosis (normal megakaryocytes) and exclude haematological malignancy.
Treatment is often not necessary. Steroids and intra-venous immunoglobulin (acts by saturating the Fc receptors within the spleen) shorten the course of the condition. Prior to using steroids a bone marrow aspirate must be performed to exclude leukaemia. Platelet transfusions are not used unless life threatening bleeds occur. In refractory cases splenectomy can be considered. Previous response to intravenous immunoglobulin is suggestive of a favourable outcome of splenectomy.
In children 80% of cases are acute self limiting with a full recovery within 6 months, most within 8 weeks.