Prepared by Gregory Chipman, MD, Chief Resident, Department of Medicine, and John L. Johnson, MD, Associate Professor of Medicine, Division of Infectious Diseases, Case Western Reserve University School of Medicine, University Hospitals of Cleveland, Cleveland, Ohio

A 73-year-old woman is admitted with 4 days' duration of insomnia, anorexia, confusion, and malaise. She had also complained to family members about foul smells in her house, which no one else noted. She has rheumatoid arthritis, hypertension, and osteoporosis but denies recent illnesses and any fever, cough, rash, or dysuria. She has no history of a neurologic disease. Her medications include prednisone, 10 mg daily; lisinopril; and risedronate.

Physical examination shows she is febrile (temperature, 38.6ºC) and fully oriented but slightly lethargic. Her neck is supple. No lymphadenopathy or rash is present. Crackles are heard over the right-lower chest. Abdominal and cardiac examinations are unremarkable. Neurologic examination shows no cranial nerve deficits; her sensation and strength are intact. Laboratory test results are: white blood cell (WBC) count, 11.3 x 109/L; serum sodium, 126 mmol/L. A head computed tomography (CT) scan is normal. Lumbar puncture reveals: WBC count, 0.020 x 109/L, with 69% lymphocytes; red blood cell (RBC) count, 0.013 x 109/L; total protein level, 64 mg/dL; glucose level, 47 mg/dL. Gram's stain of the cerebrospinal fluid (CSF) is negative. A brain magnetic resonance imaging (MRI) with contast shows increased signal on T2 and fluid-attenuated inversion recovery images in the right-medial temporal lobe and adjacent areas of the right frontal lobe (Figure).

What's Your Diagnosis?

• Pneumococcal meningitis
• Listerial meningitis
• Herpes simplex encephalitis
• Stroke