When a well child comes to accident and emergency (A&E) with a history of sudden onset bruising, purpura and petechiae, and is found to have an isolated severe thrombocytopenia (TP), the diagnosis is usually obvious: acute immune thrombocytopenic purpura (ITP). But, could something more sinister be going on? Is ITP the correct diagnosis?

This article outlines the features that should make a clinician suspect there may be an alternative diagnosis. Aware of the possible differential diagnoses, the clinician can appropriately investigate and manage the child with ITP, and know when to refer to a paediatric haematologist for specialist help.

PRESENTATION

Acute ITP is an autoimmune disorder characterised by severe TP and mucocutaneous bleeding due to opsonisation and destruction of platelets by circulating antibody. The affected children are young (peak incidence is between 2 and 5 years of age) and previously well. It is often called idiopathic even though most children typically present a few days or weeks after a viral illness or vaccination.

A child with uncomplicated acute ITP:

• is usually otherwise completely well with no history of any major illness or bone pain (see point 1 below),

• is most commonly between 2 and 5 years of age (see point 2 below),

• presents with sudden onset of petechiae and bruising (see point 3 below),

and has

• often had a recent viral illness or vaccination,

• no family or personal history of TP or other bleeding disorders (see point 4 below),

• no splenomegaly or lymphadenopathy on clinical examination (see point 5 below),

• an otherwise completely normal blood count for age, and

• a very low platelet count (usually <20×10⁹/l, often in single figures) (see point 6 below).

Points 1–6 below are aids to working through the differential diagnoses in those atypical cases which do not fit the above description of uncomplicated ITP. …