A child with a severe case of Henoch-Schönlein purpura, courtesy Okwikikim, via Wikipedia
Henoch-Schönlein purpura, also known as IgA vasculitis, is a form of vasculitis that causes small hemorrhages (purpura) beneath the surface of the skin that can be perceived by touch. It usually also causes joint pain and abdominal pain and, in rarer cases, damage to the kidneys. The symptoms can often be set off by an infection, but can also be set off by some types of antibiotics. Although it can affect adults, it's far more common in children.
In the vast majority of cases, Henoch-Schönlein is harmless and the symptoms will disappear in a few weeks. However, in about a third of cases, the symptoms spontaneously return after they resolve themselves. As such, treatment is usually focused on relieving the symptoms. However, in about one of a hundred cases, the disease can cause irreversible damage to the kidneys. In those cases, either blood or protein will be present in the urine. In those cases, steroids and cyclophosphamide can be used to reduce the immune response and prevent further damage.
Some of the complications of Henoch-Schönlein are blood in the stool and nausea from the abdominal pain.
A combination of the purpura, joint pain and abdominal pain is usually enough to confirm a diagnosis of Henoch-Schönlein. A skin biopsy may also be used for confirmation. However, care must be taken to distinguish Henoch-Schönlein purpura from hypersensitivity vasculitis.