Case 334.

History: A 30-year-old female patient who was 25 weeks pregnant presented to the emergency department with a 1-month history of mild headache and 2 weeks of progressive somnolence and photophobia accompanied by binocular horizontal diplopia and right gaze deviation. The patient also described new neck pain with passive head movements, without neck stiffness. Overall, the pregnancy was uncomplicated, with no high-risk features. Fever, chills, cough, shortness of breath, and abdominal or chest pain were denied. The patient had no history of rash, intravenous drug use, immunosuppressive medication use, or documented congenital abnormalities. She had not traveled recently, although she lived in Vancouver, British Columbia, Canada, 2 years prior to presentation. There was no recent or recurrent bacterial or viral illness. At clinical examination, the patient exhibited a decreased level of alertness and appeared tired. Vital signs were unremarkable, with a normal temperature (37.1 °C). Cranial nerve assessment revealed mild right abducens nerve palsy; neurologic examination was otherwise normal. Fundoscopic examination showed moderate grade 3 papilledema, left greater than right, with obscuration of some of the vessels leaving the disk. A CT scan of the head at admission was interpreted as normal (Fig 1). MRI of the brain performed 5 days later, due to persistent symptoms, revealed infratentorial and supratentorial imaging abnormalities (Figs 2-5). Lumbar puncture revealed high cerebral spinal fluid (CSF) opening pressure (32 cm H₂O; upper limit of normal, 25 cm H₂O). The CSF was clear, and analysis revealed an elevated total nucleated cell count (136 ×10⁶/L; reference range, 0-5 ×10⁶/L), with predominant lymphocytic moderate pleocytosis (100 ×10⁶/L; reference range, 0-5 ×10⁶/L) (59% lymphocytes) and normal glucose (3.3 mmol/L; reference range, 2.2-3.9 mmol/L) and normal total protein (0.27 g/L; reference range, 0.16-0.49 g/L) levels. Blood culture results for mycobacteria and anaerobic and aerobic microorganisms showed no growth. Findings from extensive additional diagnostic workup, including serologic testing for herpes simplex virus, varicella-zoster virus, enterovirus, Brucella, Coccidioides, Histoplasma, and mycobacteria, were negative. The HIV test result was negative, and the CD4 lymphocyte count and complement and immunoglobulin levels were within normal range. Autoimmune screening results were also negative.