Henoch-Schönlein purpura (HSP) is the most common vasculitic disease of childhood. It is a multisystem disease most commonly affecting skin, joints, gastrointestinal tract, and kidneys, but other organs may be affected. Epidemiological studies have shown HSP to have an annual incidence of approximately 13.5–18/100 000 children.1 ,2 Although this is a condition that can occur from age 6 months to adulthood, 50% of cases occur in children under 5 years of age and 75% are under 10 years. In most reports HSP is more common in boys.3

The cause remains unknown although there is often an antecedent respiratory infection. Streptococcal infections have been implicated but other organisms including adenovirus, parvovirus, and mycoplasma have also been reported to precede HSP. The increased incidence in winter and spring supports an infectious trigger in a susceptible individual.

The American College of Rheumatology 1990 criteria for the classification of HSP aimed to identify diagnostic criteria to differentiate HSP from other vasculitic diseases.4 The four criteria identified, of which two are necessary to make the diagnosis, are:

• age < 20 years at onset

• palpable purpura

• “bowel angina” (diffuse abdominal pain or bowel ischaemia usually with bloody diarrhoea)

• biopsy evidence of granulocytes in the walls of arterioles or venules.

 The diagnosis is usually made after the appearance of the classic rash that primarily affects the extensor surfaces and may be urticarial or purpuric. Joint involvement occurs in 60–84% of cases and generally affects the ankles and knees. It is often the most incapacitating part of the initial illness. Gastrointestinal disease occurs in up to 76% of patients varying from colicky abdominal pain, nausea, and vomiting to intestinal haemorrhage, intussusception, pancreatitis, and hydrops of the gall bladder. There is an increased risk of renal disease in those with bloody stools.

 The reported incidence of renal …