Clinical update: Henoch-Schönlein purpura.

Henoch-Schönlein purpura (HSP) is an acute smallvessel leucocytoclastic vasculitis. HSP is the most common vasculitis in children, with an incidence of about 10 cases per 100 000 a year. In most series, boys are aff ected more often than girls. Although it can occur at any age, HSP is overwhelmingly a disease of childhood. The mean age of patients is 6 years; 75% of patients are under 8 years of age and 90% are less than 10 years of age. The clinical features of HSP may be atypical at the extremes of age. The severity tends to be milder in infants under 2 years of age and worse in adults. Most patients present from autumn to spring, and HSP often follows a respiratory infection. A wide variety of pathogens, drugs, and other environmental exposures have been associated with HSP. Of all pathogens linked to HSP, group A β-haemolytic streptococcus has been the most studied. Positive throat cultures have been reported in 10–30% of patients, and titres to anti-streptolysin O are raised in 20–50% of patients. Thus a substantial minority of patients have concomitant or recent streptococcal infection, but most cases have no direct link to streptococcal infection. Although the cause is unknown, it is clear that IgA has a pivotal role in the pathogenesis of HSP. There are two subclasses of IgA, IgA1 and IgA2, but only IgA1 is involved in HSP. The clinical manifestations of HSP are a consequence of widespread vasculitis resulting from IgA1 deposition in vessel walls and the renal mesangium. The reasons for the exclusive involvement of IgA1 in HSP remain unclear. However, IgA1, unlike IgA2, contains a hinge region with multiple O–linked glycosylation sites. Two studies showed diminished glycosylation of the hinge region of IgA1 in patients with HSP. IgA1 molecules with diminished hinge-region glycosylation are prone to aggregate into macromolecular complexes. These complexes activate the alternative pathway of complement, and then deposit in the renal mesangium. The clinical features of HSP have been amply documented in reports spanning 200 years. The major clinical features of HSP are shown in the table and other infrequent complications are shown in the panel. Cutaneous purpura is the essential element in the diagnosis of HSP. The characteristic rash consists of palpable purpuric lesions 2–10 mm in diameter. Pinpoint petechiae and coalescent echymoses may be scattered among these lesions. The purpura is concentrated on the buttocks and lower extremities, but it is not restricted to those areas. Arthritis is the second most common feature of HSP, occurring in roughly 75% of patients and most often aff ecting the knees and ankles. The joints of the upper extremities are involved in a few patients. HSP arthritis is typically painful and often inhibits walking. It is important to remember that arthritis may precede the onset of the purpura by up to a week in 15–25% of patients. Gastrointestinal involvement occurs in 50–75% of patients. Colicky abdominal pain, vomiting, and gastro intestinal bleeding are the dominant features. Gastrointestinal bleeding is usually occult, but 30% of patients have grossly bloody or melanotic stools. Intussusception has been reported in 1–5% of patients. The intussusceptions associated with HSP are ileoileal in most patients. Thus abdominal ultrasonography or computed tomography are the preferred diagnostic modalities if intus susception is suspected in a patient with HSP. Gastrointestinal signs and symptoms may precede the onset of purpura by up to 2 weeks in 10–20% of patients. Gastrointestinal symptoms before the onset of the rash may simulate several infl ammatory or surgical diseases of the bowel. The correct diagnosis becomes evident with the appear ance of the typical rash. Renal involvement occurs in 40–50% of patients. Microscopic haematuria is the most common fi nding,