Causes of Henoch-Schonlein purpura
Doctors and researchers do not know exactly what causes the inflammation of the small blood vessels, but they suspect HSP may be a reaction to an infection (an overly aggressive response by your child's immune system). Doctors have noticed that HSP often follows a viral illness, like the common cold.
Complications
About one in two children with HSP develop problems with their kidneys; most of these are mild and temporary. Only a small minority will have serious kidney disease. The primary sign of kidney problems is microscopic blood in the urine (not visible to the naked eye).
Recovery
HSP is considered a one-time illness, though children occasionally get it more than once. Most children recover completely from this illness with no long-term side effects. Recovery can take a few days up to a month.
For most children who experienced kidney inflammation, the kidneys return to normal in a few days. In some cases, however, the kidneys can remain inflamed for as long as two years.