A 58-year-old Indian man presents with a 3-week history of progressive headache, jaw claudication, and visual blurring in the left eye. On examination, his left temporal artery is tender and non-pulsatile. ESR is 92 mm/h, CRP is 8.5 mg/dL, and hemoglobin is 10.2 g/dL. Fundoscopy shows optic disc pallor. What is the most appropriate next step in management?