Sometimes in pathology, you hear the name of a disease over and over, but somehow you never really learn about it. So it was for me with Henoch-Schonlein purpura. I knew that some vasculitides resembled the lesions of Henoch-Schonlein purpura, and I knew it had something to do with IgA – but the disease itself eluded me. So, for those of us who never learned about it, here’s a quick summary of Henoch-Schonlein purpura, in 400 words or less.

Henoch-Schonlein purpura (HSP) is a systemic disease best characterized as a immune-related, small-vessel vasculitis. There are IgA- and C3-containing immune deposits in vessels and elsewhere, but the cause of these deposits is unknown. Common manifestations include:

• Purpuric skin lesions
• Abdominal manifestations
• Arthritis
• Renal manifestations

HSP is most common in children between 3 and 8. In fact, it is the most common vasculitis of childhood, with an incidence of 20 per 100,000 children each year. The disease occurs in adults too, but much less frequently. Many patients have a strong history of atopy, and disease usually appears following an upper respiratory tract infection. Although the exact cause of the disease is unknown, it may be that the deposition of IgA and C3 is related to an overzealous immune response to a preceding infection.

The classic triad of HSP is purpura, arthritis and abdominal pain – but as with many classic triads, not all patients have all three symptoms. All patients with HSP have the skin lesions, 80% have arthritis or joint pain, and 60% have abdominal pain.

The skin lesions consist of subepidermal hemorrhages and a necrotizing vasculitis involving the small vessels of the dermis. They usually appear over the extensor surfaces of the arms and legs, and sometimes the buttocks (as in the photo above). The abdominal manifestations include pain, vomiting, and intestinal bleeding. Vasculitis may be present in the GI tract too.

Renal manifestations occur in about 1/3 of patients. The most common symptom is hematuria (either gross or microscopic) – but a small number of patients develop nephritic or nephrotic syndrome. When HSP occurs in adults, the renal manifestations are more severe and may evolve into a rapidly progressive, crescentic glomerulonephritis. By immunofluorescence, there is prominent deposition of IgA (and sometimes IgG and C3) in the mesangial region. In fact, the pattern looks so much like the pattern you see in IgA nephropathy that it’s probably best to think of HSP and IgA nephropathy as different manifestations of the same disease.

Treatment is usually symptomatic, involving pain killers for the abdominal and joint pain. Steroids may reduce the chance of severe renal disease, but they are used sparingly. The prognosis in kids is excellent (upwards of 90% of children recover completely), and it’s almost as good in adults. In some cases, the disease recurs, usually manifesting with bouts of hematuria, but in most cases, the disease resolves completely.