A 72-year-old woman with hypertension presents with a 4-month history of lower back discomfort that radiates to both buttocks and lateral thighs. Previously, she walked 2 miles (3.2 km) a day; now she has difficulty walking two blocks and standing up for more than 15 minutes at a time. Her physical examination is notable only for a slightly stooped posture and a reduction of vibratory sensibility in both great toes. How should she be evaluated and treated?