Question category: Respiratory
A 28 year old gentleman has a long history of rhinitis and asthma. However he now presents with haemoptysis. He has also noticed a rash and severe pain which he states feels like sciatica. He is feeling generally unwell with fatigue, myalgia and weight loss. On examination he is hypertensive and there is a purpuric rash. Bloods reveal acute renal failure and elevated inflammatory markers and eosinophil count. Given the most likely diagnosis, which antibody is likely to be present?