Definition of Henoch-Schonlein purpura:

Henoch-Schonlein purpura is a disease that involves purple spots on the skin, joint pain, gastrointestinal problems, and glomerulonephritis (a type of kidney disorder).

Causes, incidence, and risk factors:

Henoch-Schonlein is a type of hypersensitivity vasculitis and inflammatory response within the blood vessel. It is caused by an abnormal response of the immune system. It is unclear why this occurs.

The syndrome is usually seen in children, but it may affect people of any age. It is more common in boys than in girls. Many people with Henoch-Schonlein purpura had an upper respiratory illness in the previous weeks.