DefinitionHenoch-Schonlein purpura is a disease that involves purple spots on the skin, joint pain, gastrointestinal problems, and glomerulonephritis (a type of kidney disorder).Alternative NamesAnaphylactoid purpura; Vascular purpuraCauses, incidence, and risk factorsHenoch-Schonlein 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 weeks before.SymptomsAbdominal painJoint painPurple spots on the skin (purpura), usually over the buttocks, lower legs, and elbowsBloody stoolsHives or angioedemaNauseaDiarrheaPainful menstruationVomitingSigns and testsThe doc