Focal neurologic signs in western equine encephalitis.

Focal neurologic signs developed in a 75-year-old woman who had presented with encephalitis. A diagnosis of western equine encephalitis was made from serologic findings. Although she was improving clinically the patient died from acute dissection of an aortic aneurysm 11 days after admission to hospital. The pathological findings--perivascular infiltrates and multifocal necrosis in the deep grey matter--were consistent with the diagnosis of western equine encephalitis. Similar findings in the basal ganglia and spinal cord corresponded to the focal clinical signs.