Could you explain what is henoch shonlien purpura sicknes?

Rare immune disorder: Common in kids, manifests as skin red rash, arthritis and abdominal pain which resolves spontaneously in most usually in 4 mos, but may have persistence and organ involvement in some, such as kidneys etc. Elevated reactive proteins CRP usually seen. Exact cause unknown but may happen after infections.Adults may have kidney injury.Biopsy of skin or kidney may be diagnostic. Treatment is symptomatic