A 64-year-old man is evaluated in the emergency department for progressively deteriorating mental status. His wife states that he has been experiencing episodic headaches during the past several months, and his mental status has changed progressively over the past several days. History is significant for atherosclerosis, hypertension, and coronary artery disease. He has a 40-pack-year history of smoking. Medications are atorvastatin, lisinopril, and low-dose aspirin.
On physical examination, the patient is alert and oriented to self but not to place or year. Vital signs are normal. BMI is 26. On the Mini–Mental State Examination, he is unable to do serial sevens, is able to recall only one object out of three, and cannot draw a geometric figure that is shown to him. The remainder of the examination, including the neurologic assessment, is within normal limits.
Laboratory studies, including complete blood count, basic metabolic panel, liver chemistries, and urinalysis, are normal; erythrocyte sedimentation rate is 22 mm/h.
Lumbar puncture is performed; cerebrospinal fluid analysis reveals a leukocyte count of 15/µL (15 × 106/L), 90% lymphocytes, and a protein level of 45 mg/dL (450 mg/L).
Chest radiograph is unremarkable. A brain MRI shows scattered lesions, mainly in the white matter, and an MR angiogram shows possible narrowing of the intracerebral arteries.
Which of the following is the most appropriate next step in management?