Usually preschool but any age! Boys more than girls. Vasculitis.
A vasculitis with systemic features, but usually benign. Urticarial rash becoming purpuric but still raised (pathognomic), extensor surfaces of lower limbs incl buttocks, sometimes trunk and limbs, scrotum, rarely face (infant). Can be blistering, note swollen ankles/feet (arthropathy).