Henoch-Schönlein purpura (HSP) is also known as anaphylactoid purpura or purpura rheumatica. It is a leukocytoclastic vasculitis affecting small blood vessels in virtually any organ system, but predominantly the skin, joints, and kidneys. HSP is the most common type of childhood systemic vasculitis, with an annual incidence of 10 to 20 per 100,000 children less than 17 years of age and a slight male predominance.1 Most patients are between the ages of 3 and 10 years, with the peak age of onset 4 to 6 years. The clinical course is usually benign and self-limited, although a small proportion of patients may have significant long-term sequelae, mainly as a result of renal involvement.
Immunoglobulin A (IgA) levels are characteristically elevated in HSP, but the pathophysiologic process leading to leukocytoclasis is incompletely understood. Environmental and genetic factors also play a role. HSP often follows infections, most commonly streptococcal upper respiratory tract infections, explaining the preponderance of HSP cases in in the fall, winter, and spring. Other triggering factors include immunizations, medications, or insect bites. The rate of HSP is higher in patients with certain complement deficiencies and those with a mutation in the gene associated with familial Mediterranean fever, the MEFV gene.2
Biopsy of affected organs is not often undertaken unless the diagnosis is in question or the severity of renal involvement requires additional information to direct therapy (see Diagnostic Evaluation, below). Pathologic examination of involved tissue early in the process reveals evidence of immune-complex-mediated leukocytoclastic vasculitis. There is a perivascular infiltrate of neutrophils and mononuclear cells around necrotic small blood vessels. Immunofluorescence and electron microscopy may reveal deposits of IgA, C3, and fibrin. If the biopsy is delayed, findings will be nonspecific, as prolonged compromise of vascular integrity allows leakage of all plasma elements.
HSP is marked by the classic triad of nonthrombocytopenic palpable purpura, arthritis, and abdominal pain. Renal involvement may be reflected by the presence of hematuria or proteinuria, which is often mild. In rare cases, renal involvement may progress to chronic renal failure.
The typical history is of an otherwise well child presenting with a constellation of symptoms of rash, arthralgia, and colicky abdominal pain 1 to 3 weeks after an upper respiratory infection. Malaise or a low-grade fever may precede the classic symptoms by a few days. The three symptoms may occur concurrently or develop within days, and occasionally weeks, of each other. The classic rash and joint pain alone, or rash and abdominal pain, may be sufficient to make the diagnosis.
In three-quarters of affected children, a rash is the initial presenting feature of HSP. It is characteristically a symmetric, dark red or purple, non-blanching palpable exanthem. The lesions are usually not painful but occasionally may be pruritic (Figure ...