A Peculiar Type of Postencephalitic Epilepsy: Second Report

Abstract

Purpose: During postencephalitic epilepsy (PEE), epileptic seizures usually appear a few to several months after the acute encephalitis (AEs) or encephalopathy (AEp). At the International Congress of EEG & Clinical Neurophysiology (1990), we proposed a new type of PEE with these two characteristics: (a) seizures persist through the acute, convalescent, and chronic stages, with no seizure‐free interval, making the discrimination between the acute‐stage seizures and the AEs or AEp sequelae difficult; and (b) highly intractable partial seizures. Subjects and Methods: We have now studied the prognosis of our cases for 7 years after the first report, and resummarized the characteristics of this type of PEE, including similar cases reported in Japan after our proposal. This analysis includes our six cases and 24 other reported cases. Results: Our cases: present age, 9–16 years. Present seizure frequency; daily, three patients; weekly, one; monthly, one; and yearly, one. Seizure type: partial seizures ± secondary generalization (GTS). DQ: <25, three patients (severe communication disorders, two; 25–50, one; and 5S70, two. This new type of PEE accounted for 5–8% of the total AEs or AEp at three institutions. Age at onset of seizures, 3–15 (M, 8 ± 4) years. All but one had previously been completely healthy children with no history of seizures. Seizures with fever after preexisting illness occurred f consciousness disturbance. Seizure types included clusters of complex partial seizures (CPS) ± GTS resistant to all forms of treatment, including drip intravenous injection (DIV) of diazepam, phenytoin, lidocaine, and barbiturates under mechanical ventilation. The highly intractable CPS continued. Mental deterioration was seen in all cases. Motor deficits were seen only in one case whose age at seizurem onset was 2 years, the youngest case in our series. Five died during the chronic stage: four sudden deaths (due to seizures?) and one suicide, Pleocytosis in the cerebrospinal fluid (CSF) was negative or minimal in most cases. Thorough viral and metabolic studies, including the polymerase chain reaction (PCR) method have failed as yet to reveal the etiology. Interictal EEG showed generalized high‐voltage slow waves without spikes during the acute phase and multifocal spikes during the convalescent phase. Computed tomography (CT) and magnetic resonance imaging (MRI) scans revealed diffuse cerebral atrophy during the convalescent phase. Conclusions: It is difficult to discriminate between the seizures during the acute phase of AEs and the sequelae of AEs. The critical point is “when did epileptogenesis develop?” One possibility is that intractable seizures continued because of AEs with strong epileptogenesis followed by seizures due to AEs sequelae. These patients were similar to those reported by Brett (1967) in terms of both status epilepticus and encephalitis. However, the frequency, seizure mode, and severity of the sequelae were much greater in our group. We can also exclude Rasmussen syndrome, as none of our patients showed progressive paresis and epilepsia partialis continua. In Japan, this type of PEE has received attention, and similar case reports have been published. However, there have as yet been no reports in the international literature. This group might be categorized as AEs of unknown origin. In fact, the unknown group had a higher frequency of secondary epilepsies, than other groups of AEs (Gibbs and Gibbs, 1964). The etiology might be viral encephalitis with strong epileptogenesis and poor CSF pleocytosis, except in the case of herpes simplex virus. We recommend that such patients be started on barbiturate therapy under intensive care unit (ICU) management as promptly as possible. This intractable epilepsy group merits close attention.