A 19-year-old man with a history of recent-onset asthma presents with chest pain, intermittent claudication and respiratory distress that is unresponsive to bronchodilators and antibiotics. Physical examination reveals mild hypeension (blood pressure = 150/100 mm Hg), bilateral wheezing and numerous purpuric skin lesions on the feet. Laboratory studies demonstrate that leukocytes are increased to 14,000/mL with increased eosinophils and platelets are increased to 450,000/mL. BUN is elevated to 30 mg/dL, and serum creatinine is elevated to 3.5 mg/dL. The serum antineutrophil cytoplasmic antibody test is positive. Urinalysis discloses 3+ proteinuria and RBCs. A renal biopsy demonstrates vasculitis of medium-sized aeries, accompanied by eosinophilia. Which of the following is the most likely diagnosis?