A 33-year-old woman is evaluated in the emergency department for a 2-month history of fever, lethargy, weight loss, and headache. She moved to the United States from India 4 years ago. Her father died of tuberculosis 20 years ago. Medical history is otherwise unremarkable, and she takes no medications.

On physical examination, temperature is 38.6 °C (101.5 °F), blood pressure is 114/70 mm Hg, pulse rate is 94/min, and respiration rate is 18/min. BMI is 20. Except for lethargy, neurologic examination is unremarkable. No abnormalities are noted on ophthalmologic, cardiac, or pulmonary examinations or in the remainder of the physical examination.

Cerebrospinal fluid (CSF) studies:

Leukocyte count

275/µL (275 × 106), with 98% lymphocytes

Glucose

30 mg/dL (1.7 mmol/L)

Protein

250 mg/dL (2500 mg/L)

CSF opening pressure

150 mm H2O

The remainder of a complete blood count and comprehensive metabolic panel are normal. Acid-fast bacilli smear of CSF is negative, but polymerase chain reaction is positive for Mycobacterium tuberculosis.

Minimal basilar meningeal enhancement is seen on CT scan of the head without any evidence of cisternal or ventricular abnormalities, midline shift, or mass lesion.

In addition to four-drug antituberculous therapy, which of the following is the most appropriate additional treatment?