A 21-year-old immunocompetent man who was a long-term resident of Qatar presented to the emergency department with recurrent episodes of unprovoked generalized tonic-clonic seizures lasting 2–3 minutes that spontaneously resolved and were associated with postictal confusion. The patient also had progressive mild diplopia, intermittent dizziness, and numbness in the left arm over the course of 3 months. The patient did not have any other systemic symptoms or chronic medical diseases. He did not have any history of intake of illicit drugs, supplements, or regular medications; he had not received any recent vaccinations; and he had not undergone any surgical procedures. He had no history of travel. At presentation, vital signs were normal. Neurologic examination showed mild left homonymous hemianopia, normal gait with no cerebellar signs, and preserved sensations, power, tone, and reflexes in all four limbs. An electroencephalogram showed no epileptiform discharges. Chest CT and extensive laboratory work-up, including viral, fungal, bacterial, and parasite work-up, thyroid function tests, and immunologic blood tests yielded normal results. Those included normal complete and differential blood counts and normal serum chemistry. Serum analysis was negative for antinuclear antibody, Sjögren syndrome antigens A and B, cytoplasmic antineutrophil cvtoplasmic antibody, and paraneoplastic profile. Serum evaluation was also negative for human immunodeficiency virus type 1 and type 2 RNA, and Brucella, Schistosoma, and toxoplasma antibodies. Venereal Disease Research Laboratory (VDRL) and rapid plasma regain (RPR) test results were negative. Cerebrospinal fluid (CSF) analysis revealed clear fluid and normal pressure and biochemistry, except for elevated protein concentration (0.48 g/L) (normal range, 0.15–0.45 g/L). There were 43 leukocytes/µL (99% lymphocytes) (normal range, 0–5 leukocytes/µL; lymphocytes range, 40%–80%), with no atypical or malignant cells. CSF Gram staining, acid-fast staining, cryptococcal antigen, varicella-zoster virus polymerase chain reaction (PCR), herpes simplex virus PCR, VDRL, and RPR test results were negative. CSF cultures did not show any evidence of growth of bacteria, fungi, or acid-fast bacillus. CSF flow cytometry did not show a monoclonal lymphoid population. No CSF oligoclonal bands were detected. Conventional brain MRI with intravenous administration of contrast material and a perfusion study were performed and included different sequences (Figs 1–3).Initial brain MRI demonstrated T2 fluid-attenuated inversion recovery (FLAIR) hyperintensity in the right parieto-occipital subcortical and periventricular white matter, extending to involve the right side of the splenium of the corpus callosum, with only minimal mass effect and T2 FLAIR tiny iso- and hypointensities within the hyperintense area (Fig 1A, 1B). This area demonstrated a patchy nodular and curvilinear peppering contrast enhancement pattern that was limited to supratentorial structures (Fig 2). The larger enhancing nodules that had low signal intensity on T2 FLAIR images had slightly high signal intensity on diffusion-weighted images with a similar apparent diffusion coefficient (Fig 3A, 3B). Brain perfusion MRI revealed a decrease in perfusion in the area (Fig 3C). Over the next 6 months, the patient’s symptoms improved after appropriate treatment and followup, with no relapse of seizures. Follow-up brain MRI was performed (Fig 4). What is your diagnosis?