Henoch-Schonlein purpura (anaphylactoid purpura)

Henoch-Schonlein purpura (anaphylactoid purpura) is an old disease, described first in the 1700's. It is an inflammation (vasculitis) of the smallest blood vessels throughout the body. It is characterised by

a distinctive purpuric rash rash most pronounced on the legs and buttocks
gastrointestinal symptoms of pain and gastrointestinal bleeding, with possible complications of bowel rupture or intussusception
kidney involvement (nephritis)
joint symptoms (arthritis)
angioedema - massive transient swelling of the scalp, eyelids, lips, ears, backs of the hands and feet, back, scrotum, and perineum is common and may be striking, especially in young children

It has no known cause. It often at least seems to be triggered by recent respiratory infections, perhaps viral or streptococcal. It occurs at any age, but is much more common in children than adults; most cases occur between 2 and 8 years of age. There is a 2:1 prediliction for boys.

The disease may begin suddenly, with rash, abdominal pain, and other signs, or it may take a more insidious course over a period of weeks. The rash seems to be the constant feature; it is always present as far as we know. The classic rash begins looking rather like urticaria (hives). the rash evovles to become more petechial or purpuric. The purpuric areas evolve in the usual manner of a bruise and eventually fade away. You can feel these areas under the skin.

Arthritis, especially of the large joints such as knees and ankles, occurs in the majority of cases. The affected joints are generally tender, swollen, and painful. The arthritis usually resolves after a few days without residual damage but may recur during flareups.

Kidney disease occurs in up to half of affected children, usually manifest by blood and protein in the urine. While more severe kidney involvment can occur and may even become more or less permanent, most children with kidney involvement recover fully. A very few patients do not clear up fully and may go on later to develop more serious chronic kidney disease.

HS purpura is usually a mild illness which only lasts a few days, however, a few children have more serious and prolonged courses of up to a year or more of periodic flareups. There is no specific treatment at this time; care is supportive and any complications are generally managed conservatively.