Extensive laboratory investigations showed increased levels of C-reactive protein and leukocytes and mild hyponatremia. Serological test results for Epstein-Barr virus, cytomegalovirus, hepatitis B and C, Borrelia, Treponema, Toxoplasma, and human immunodeficiency virus were negative. Brain magnetic resonance imaging (MRI) demonstrated multiple disseminated lesions in both hemispheres, the basal ganglia, pons, and cerebellum that were hyperintense on T2-weighted and fluid-attenuated inversion recovery images and hypointense on T1-weighted series with contrast enhancement (Figure 1). Based on these findings, a cerebral infectious process, neoplastic disease, or autoimmune-mediated disease were considered. Cerebrospinal fluid (CSF) examination showed a mild pleocytosis (total white blood cell count, 6.7/mm3; 75% monocytes, 25% polymorphs) with normal protein and glucose concentrations and an IgG index of 0.5 (IgG level, 0.048 g/L). Results of extensive virological and bacteriological testing of CSF, including herpes simplex types 1 and 2, cytomegalovirus, varicella zoster virus, Epstein-Barr virus, JC virus, Enterovirus, Parechovirus, routine aerobic and anaerobic bacterial culture, Toxoplasma, Legionella, Borrelia, Cryptococcus, Mycobacterium, and Treponema, as well as levels of paraneoplastic antibodies (Anti-Hu, Anti-Jo, Anti-Ri, Anti-Tr, Anti-Amfi, Anti-CV2, and Anti-Ma2) and 14.3.3 protein, were negative. On cytological analysis of the CSF, no malignant cells were found. Anti–myelin-oligodendrocyte-glycoprotein antibodies in serum were negative. A computed tomographic scan of the thorax and abdomen and transesophageal echocardiography did not reveal any abnormalities. Results of blood cultures and L pneumophila urinary antigen serogroup 1 testing were negative.