A 47-year-old man presents with a 5-month history of persistent nasal congestion and recurrent nosebleeds; examination reveals collapse of the nasal bridge. Over the past 6 weeks he has developed a productive cough with blood-tinged sputum, and chest CT shows bilateral cavitary nodules. He reports decreased urine output; urinalysis demonstrates RBC casts and 2+ proteinuria, and his creatinine has risen from 1.0 to 3.2 mg/dL over 3 weeks. He has no history of asthma and has never wheezed. He is a non-smoker. Temperature 37.8°C, ESR 92 mm/hr. ANCA serology shows a cytoplasmic staining pattern on indirect immunofluorescence at high titer; the perinuclear pattern is absent.
Which of the following is the most likely diagnosis?