Progressive MRI findings of West Nile virus encephalitis in a patient with diabetes mellitus.

A man in his 70s was admitted to our hospital with complaints of fatigue, loss of appetite and fever. His neurological examination was normal. He had a medical history of diabetes mellitus for 25 years. Urine analysis showed many leucocytes. Empirical antibiotic treatment was started for urinary system infection. Three days later, his mental status worsened with confusion and disorientation. MRI of the brain was normal. Two days later, the patient was intubated because of respiratory insufficiency. MRI showed restricted diffusion in bilateral thalamic nuclei. Encephalitis and ischaemia were considered in the differential diagnosis. Cerebrospinal fluid IgM antibody for West Nile virus was positive. Sixteen days later, cranial nerve reflexes were lost. MRI showed restricted diffusion and increased T2 signal intensity in the dorsal medulla and increased T2 signal intensity without diffusion restriction in bilateral substantia nigra and dentate nuclei. He died of cardiac arrest 40 days after hospitalisation.