A 40-year-old woman presents with bilateral conductive hearing loss, palpable purpura on the legs and hemoptysis. CT scan of the chest shows few thin-walled lung cavities bilaterally. Fuher investigations reveal total leukocyte count 12,000/mm3, red cell casts in the urine and, serum creatinine 2.3 mg/dL. What is the most probable diagnosis?