A 65-year-old woman with a history of fever, night sweats, fatigue, and weight loss, presents with cognitive deterioration and headache. Laboratory abnormalities include an elevated erythrocyte sedimentation rate, anemia, and elevated serum soluble interleukin 2 receptor, lactate dehydrogenase, and β2 microglobulin levels. Cerebrospinal fluid analysis demonstrates a mildly increased leukocyte count and total protein concentration. Magnetic resonance imaging showed multiple cerebral infarctions, cerebral angiography suggests vasculitis; imaging studies of the chest and abdomen and ophthalmologic evaluation were unremarkable. What would you do next?