It is the purpose of this paper to present an electroencephalographic study on Japanese B encephalitis for elucidating its pathophysiology, aiding its diagnosis and treatment and for evaluating its prognosis.
Electroencephalograms of 19 patients admitted to our clinic were investigated in their courses of Japanese B encephalitis.
We clinician have had only one method to know cerebral pathology in encephalitis, that is to judge on neurological signs and symptoms, and yet it is not entirely reliable. However, EEG can disclose pathological process which has been taken place and is going on in the acute stage in the brain of the patient and we can grasp whole pathology objectively by EEG. Besides this, we suppose we can know the prognosis of the patients more accurately by reading EEG than other conventional methods.
In the acute stage, there is a bilateral symmetric monorhythmic continuous high voltage delta activity of 1 to 2.5c/s with frontal dominancy. This pattern is very characteristic of the Japanese B encepaalitis. This finding suggests that the primary lesion of this disease is located in the subcortical structure, especially in the ascending reticular formation of the brain stem.
Electroencephalographic findings in the process of Japanese B encephalitis are illustrated in Table 1
Patients recover from encephalitis with the EEG findings in the order of 1) to 7) (from up to down) shown on the Table 1. in his EEG if the patient follows uneventful course.
We have confirmed it takes about 1 year for the patient to follow the above-mentioned process and finally attain normal EEG. This is quite different from in the case of aseptic meningitis.
If the patient fails to follow the above-mentioned course and stop at some stage in the middle, we consider this patient has much possibility to develop mental deficiency or other nourological sequelae.
In the case that patient shows epileptic discharge in his EEG during convalescent period, we predict this patient will develop clinical epilepsy sooner or later.
We, therefore, think it very important to have successive EEG study at least for four years on the patient with encephalitis even after his clinical abnormality clears up.