Background Eastern equine encephalitis occurs principally alongthe east and Gulf coasts of the United States. Recognition ofthe neuroradiographic manifestations of eastern equine encephalitiscould hasten the diagnosis of the illness and speed the responseto index cases.
Methods We reviewed all cases of eastern equine encephalitisreported in the United States between 1988 and 1994. The recordsof 36 patients were studied, along with 57 computed tomographic(CT) scans and 23 magnetic resonance imaging (MRI) scans from33 patients.
Results The mortality rate was 36 percent, and 35 percent ofthe survivors were moderately or severely disabled. Neuroradiographicabnormalities were common and best visualized by MRI. Amongthe patients for whom MRI scans were available, the resultswere abnormal for all eight comatose patients as well as forall three noncomatose patients who subsequently became comatose.The CT results were abnormal in 21 of 32 patients with readablescans. The abnormal findings included focal lesions in the basalganglia (found in 71 percent of patients on MRI and in 56 percenton CT), thalami (found in 71 percent on MRI and in 25 percenton CT), and brain stem (found in 43 percent on MRI and in 9percent on CT). Cortical lesions, meningeal enhancement, andperiventricular white-matter changes were less common. The presenceof large radiographic lesions did not predict a poor outcome,but either high cerebrospinal fluid white-cell counts or severehyponatremia did.
Conclusions Eastern equine encephalitis produces focal radiographicsigns. The characteristic early involvement of the basal gangliaand thalami distinguishes this illness from herpes simplex encephalitis.MRI is a sensitive technique to identify the characteristicearly radiographic manifestations of this viral encephalitis.
Source Information
From the Infectious Disease Division (R.L.D., S.J.T.) and the Channing Laboratory (R.L.D.), Department of Medicine, and the Department of Radiology (L.H., A.A.Z.), Brigham and Women's Hospital and Harvard Medical School, Boston.
Address reprint requests to Dr. Deresiewicz at the Channing Laboratory, 181 Longwood Ave., Boston, MA 02115.
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