Eosinophilic granulomatosis with polyangiitis (EGPA; also known as Churg-Strauss syndrome [CSS] or allergic granulomatosis) is a rare autoimmune condition that causes inflammation of small and medium-sized blood vessels (vasculitis) in persons with a history of airway allergic hypersensitivity (atopy). Effective treatment of EGPA requires suppression of the immune system with medication. This is typically glucocorticoids, followed by other agents such as cyclophosphamide or azathioprine.