Amnesia in acute herpetic and nonherpetic encephalitis

L. Hokkanen, O. Salonen and J. Launes
Department of Neurology, University of Helsinki, Finland. hokkanen@launes.pp.fi

OBJECTIVES: To evaluate how often global amnesia syndrome is encountered as a sequel of herpes simplex virus type 1 encephalitis (HSVE) and in other types of acute encephalitides, and to evaluate whether there are qualitative differences in amnesia caused by different encephalitides. SUBJECTS: Forty-five consecutive patients with encephalitis (mean age, 40.8 years) studied prospectively within a 5-year period, 8 of whom had HSVE. There were 24 normal controls. MEASURES: Neuropsychological assessment and memory evaluation after the acute stage of encephalitis, as well as at follow-up after 27.7 +/- 18.6 months. RESULTS: Three patients (6%), including 1 with HSVE, had persistent anterc grade and retrograde memory defects, typical features of global amnesia. Twelve patients had anterograde amnesia in the first assessment. No statistically significant differences in the memory measures were found between the HSVE (n = 4) and the non-HSVE (n = 8) groups. Some patients had predominantly semantic difficulty, some had a "frontal-type" memory disorder, and in some patients rapid forgetting was the prominent feature. CONCLUSIONS: The frequency of amnesia can reliably be evaluated only in consecutive series of patients. Previous literature, mainly case reports, may give the impression that global amnesia is a common consequence of encephalitis. Our findings do not support that view. Furthermore, there are clear differences in the quality of the memory impairment between cases of acute encephalitides. Our findings suggest that amnesia as a consequence of encephalitis, even HSVE, should not be considered a uniform phenomenon.