Masie is 8 years old and brought to the Emergency department by her mother Clara. Masie has developed a non-itchy rash on her lower legs earlier today. She has also complained of intermittent headaches over the last week which appear to have settled and did have some vague abdominal pain 2 days ago. There is no photophobia, neck stiffness, vomiting or fevers.
On examination she has a symmetrical purpuric rash which is also present on her buttocks. Abdominal and neurological examinations and observations are normal.
What is the most likely diagnosis?