A 4-year old boy presents with a history of left ankle joint swelling and pain for four days. It was preceded by an upper respiratory infection. On examination, the left ankle is swollen and tender. There is a petechial rash over the lower limbs. He is admitted two days later with bleeding per rectum. The most likely clinical diagnosis is:

Features of HSP are: 1. Aetiology is not known. 2. The hallmark of the disease is rash that progresses to petechiae or purpura. It is more prominent over the extensor aspect of lower extremities and buttocks. 3. Ahritis is seen in two-thirds of children and is localized to ankles and knees. 4. Abdominal pain and vomiting are common. 50% have occult blood in stool. Diarrhoea (with or without visible blood loss) or haematemesis are however' less common. 5. Renal involvement is seen in 25 to 50% of cases. 6. CNS involvement is rare but has potentially serious outcome.