EGPA is defined by eosinophil-rich and necrotizing granulomatous inflammation (often involving the respiratory tract) and necrotizing vasculitis predominantly affecting small to medium vessels. The clinical features are thought of as having three phases: an allergic phase (asthma, nasal polyps, rhinosinusitis), an eosinophilic phase (peripheral and tissue eosinophilia), and a vasculitic phase (nerve, skin, lung, kidney, GI tract, and heart). Although these phases may not be sequential, the median time from asthma symptoms to necrotizing vasculitis is 3 to 4 years. To date, there are no established diagnostic criteria for EGPA; the diagnosis is based on the constellation of clinical findings and the exclusion of other possible causes. Although an association between EGPA and antimyeloperoxidase-/peri-nuclear ANCA exists, only about 40% of patients with EGPA are ANCA positive. Some studies have found ANCA-positive EGPA to be associated with glomerulonephritis, whereas patients who are ANCA negative more commonly have cardiac involvement.