Snapshot A 35-year-old man presents to his primary care physician for numbness and weakness of the left lower extremity and "cold-like" symptoms. He has also noticed skin changes in the affected leg. His medical history is significant for asthma treated with albuterol. Physical exam is significant for 3/5 strength throughout the lower extremity and decreased touch sensation. There are cutaneous and subcutaneous nodules. Laboratory findings are significant for positive MPO-ANCA/p-ANCA antibodies and a serum eosinophil level of 8000/μL. Introduction Definition a multisystem small and medium-sized artery necrotizing vasculitis characterized by rhinosinusitis asthma peripheral blood eosinophilia Epidemiology Demographics 20-40 years of age male > female ETIOLOGY Pathogenesis unknown Presentation Symptoms/physical exam disease phases prodromal atopic disease asthma allergic rhinitis eosinophilic peripheral blood eosinophilia eosinophils infiltrate organs (e.g., lungs) vasculitic vascular and extravascular granulomatosis e.g., fever, weight loss, and skin lesions (tender subcutaneous nodules) Other findings peripheral neuropathy gastrointestinal involvement Studies Labs positive MPO-ANCA/p-ANCA antibodies ↑ IgE level peripheral blood eosinophilia (characteristic finding) Differential Granulomatosis with polyangiitis differentiating factors positive PR3-ANCA/c-ANCA antibody upper and lower respiratory and renal involvement Temporal arteritis differentiating factors occurs in elderly patients with temporal headaches and jaw claudication high risk of blindness if untreated Treatment Medical high-dose glucocorticoids indication for induction of remission Complications Necrotizing glomerulonephritis Purpura Parenchymal disease Prognosis Improved with immunosuppressive treatment