Clinical and neuroradiographic manifestations of eastern equine encephalitis.

Background: Eastern equine encephalitis occurs principally along the east and Gulf coasts of the United States. Recognition of the neuroradiographic manifestations of eastern equine encephalitis could hasten the diagnosis of the illness and speed the response to index cases.

Methods: We reviewed all cases of eastern equine encephalitis reported in the United States between 1988 and 1994. The records of 36 patients were studied, along with 57 computed tomographic (CT) scans and 23 magnetic resonance imaging (MRI) scans from 33 patients.

Results: The mortality rate was 36 percent, and 35 percent of the survivors were moderately or severely disabled. Neuroradiographic abnormalities were common and best visualized by MRI. Among the patients for whom MRI scans were available, the results were abnormal for all eight comatose patients as well as for all three noncomatose patients who subsequently became comatose. The CT results were abnormal in 21 of 32 patients with readable scans. The abnormal findings included focal lesions in the basal ganglia (found in 71 percent of patients on MRI, and in 56 percent on CT), thalami (found in 71 percent on MRI and in 25 percent on CT), and brain stem (found in 43 percent on MRI and in 9 percent on CT). Cortical lesions, meningeal enhancement, and periventricular white-matter changes were less common. The presence of large radiographic lesions did not predict a poor outcome, but either high cerebrospinal fluid white-cell counts or severe hyponatremia did.

Conclusions: Eastern equine encephalitis produces focal radiographic signs. The characteristic early involvement of the basal ganglia and thalami distinguish this illness from herpes simplex encephalitis. MRI is a sensitive technique to identify the characteristic early radiographic manifestations of this viral encephalitis.