Henoch-Schonlein purpura (HSP), also known as IgA vasculitis, is a disease of the skin, mucous membranes, and sometimes other organs that most commonly affects children. In the skin, the disease causes palpable purpura (small, raised areas of bleeding underneath the skin), often with joint pain and abdominal pain. With kidney involvement, there may be a loss of small amounts of blood and protein in the urine (hematuria and proteinuria), but this usually goes unnoticed; in a small propoion of cases, the kidney involvement proceeds to chronic kidney disease. HSP is often preceded by an infection, such as a throat infection HSP is a systemic vasculitis (inflammation of blood vessels) and is characterized by deposition of immune complexes containing the antibody immunoglobulin A (IgA); the exact cause for this phenomenon is unknown. In children, it usually resolves within several weeks and requires no treatment apa from symptom control but may relapse in a third of cases and cause irreversible kidney damage in about one in a hundred cases. In adults, the prognosis is different from in children. The average duration of cutaneous lesions is 27.9 months.For many, it tends to be relapsing-remitting over a long period of time, rather than self-limiting and there tend to be more complications sogns and symptoms: Purpura, ahritis, and abdominal pain are known as the "classic triad" of Henoch-Schonlein purpura. Purpura occur in all cases, joint pains and ahritis in 80%, and abdominal pain in 62%. Some include gastrointestinal hemorrhage as a fouh criterion; this occurs in 33% of cases, sometimes, but not necessarily always, due to intussusception. The purpura typically appear on the legs and buttocks, but may also be seen on the arms, face and trunk. The abdominal pain is colicky in character, and may be accompanied by nausea, vomiting, constipation or diarrhea. There may be blood or mucus in the stools.The joints involved tend to be the ankles, knees, and elbows, but ahritis in the hands and feet is possible; the ahritis is nonerosive and hence causes no permanent deformity.Foy percent have evidence of kidney involvement, mainly in the form of hematuria (blood in the urine), but only a quaer will have this in sufficient quantities to be noticeable without laboratory tests. Problems in other organs, such as the central nervous system (brain and spinal cord) and lungs may occur, but is much less common than in the skin, bowel and kidneys. Of the 40% of patients who develop kidney involvement, almost all have evidence (visible or on urinalysis) of blood in the urine. More than half also have proteinuria (protein in the urine), which in one eighth is severe enough to cause nephrotic syndrome (generalised swelling due to low protein content of the blood). While abnormalities on urinalysis may continue for a long time, only 1% of all HSP patients develop chronic kidney disease. Hypeension (high blood pressure) may occur. Protein loss and high blood pressure, as well as the features on biopsy of the kidney if performed, may predict progression to advanced kidney disease. Adults are more likely than children to develop advanced kidney disease ref Harrison20th edition pg 2134