Henoch-Schönlein Purpura

Definition/diagnostic criteria Henoch-Schönlein purpura (HSP), also known as IgA vasculitis, is primarily characterised as a small-vessel vasculitis. It involves the deposition of IgA-dominant immune complexes in small vessels, leading to symptoms mainly in the skin, joints, gastrointestinal tract and kidneys. The diagnosis is typically clinical, based on the combination of palpable purpura without thrombocytopenia, abdominal pain, arthritis or arthralgias, and renal involvement.

Epidemiology HSP is the most common vasculitis in children, with a peak incidence between the ages of 4 and 6 years. It is less common in adults, but the severity, especially renal involvement, may be greater in this population. There is a slight male predominance. Incidence rates in the UK are estimated at about 20 cases per 100,000 children annually. Seasonal variations have been noted, with increased incidence in the autumn and winter.

Diagnosis
Clinical features: The hallmark of HSP is palpable purpura, typically appearing on the buttocks and lower extremities. Other common symptoms include:

• Abdominal pain: Often colicky in nature, can be accompanied by vomiting and occasionally by gastrointestinal bleeding.
• Arthritis or arthralgias: Usually affecting the large joints.
• Renal involvement: Ranging from microscopic haematuria and/or proteinuria to nephritic syndrome or rapidly progressive glomerulonephritis.

Investigations: While the diagnosis is mainly clinical, investigations are important to assess the extent and severity of the disease and to monitor for complications:

• Full blood count, ESR, and CRP to assess for inflammation.
• Renal function tests and urinalysis, to detect renal involvement.
• Abdominal ultrasound may be indicated if there is significant abdominal pain, to rule out intussusception.
• Skin or renal biopsy. Demonstrating IgA deposition confirms the diagnosis, typically reserved for atypical cases or to assess the extent of renal involvement.

Treatment Management is largely supportive and symptomatic. Specific interventions include:

• Adequate hydration and pain relief.
• Corticosteroids may be used in cases with severe symptoms, particularly with significant renal or gastrointestinal involvement. However, the benefits in mild disease are uncertain.
• Immunosuppressive agents can be considered in severe or recurrent cases, especially with significant renal involvement.
• Blood pressure control and renin-angiotensin system blockade in cases with significant renal disease.

Prognosis The prognosis for HSP is generally good, especially in children, with most cases resolving spontaneously within a month. However, approximately a third of paediatric cases may have one or more relapses. Long-term complications are rare but can include chronic kidney disease, especially in adults or those with significant renal involvement at onset. Regular follow-up is important to monitor for renal complications.