Acute Encephalitis or Encephalopathy Present with Frequent Complex Partial Seizures That Directly Evolve to Partial Epilepsy: A Clinical Study of Five Pediatric Cases

Abstract

Purpose: Attention has recently been directed to pediatric cases of a peculiar type of postencephalitic or encephalopathic epilepsy proposed by Awaya et al. This type is characterized by an abrupt onset of frequent refractory complex partial seizures followed by the development of partial epilepsy. There is no seizure‐free interval, and the seizure‐type is fundamentally the same as that in the acute phase. Therefore, it is hard to distinguish the encephalitis/encephalopathy‐related seizures from epileptic ones as its sequela. The pathomechanism of this syndrome remains unknown, even though viral infection has been postulated. After studying our cases, we looked for those in this category to elucidate its clinical characteristics. Methods: Five cases (two boys and three girls) with this syndrome were selected for this study from 53 pediatric patients with acute encephalopathy or encephalitis. These patients had been treated at Sendai City Hospital during the years from 1986 to 1996. This is an incidence of 9.4%. Clinical features such as cerebrospinal fluid and EEG findings, neuroimaging, prognosis of epileptic seizures, and mental status were investigated. Results: The age at onset ranged from 4 to 14 years. All cases had no significant previous or family history. In all cases, there was an antecedent infection. Seizure type during the acute phase consisted of complex partial seizures with or without secondarily generalized tonic‐clonic convulsions. All had a high fever during the acute stage. The interictal EEG revealed generalized high‐voltage slow waves, and the ictal EEG showed diffuse spike‐and‐wave discharges developing from temporal or occipital spike foci. Mild cerebrospinal fluid pleocytosis was noted in two cases. The five cases were divided into two groups according to their clinical severity. In the severe group (three cases), the seizures during the acute phase were highly refractory. Pentobarbital (PTB) was administered to two of the three cases. The duration of the acute phase ranged from 1 to 5 months. The computed tomography (CT) and magnetic resonance imaging (MRI) showed diffuse cerebral atrophy. In one case, localized lesions also were detected in the right temporal and both occipital lobes. The lesions coincided with EEG spike foci, which persisted throughout the course. All three had profound mental deterioration and intractable partial epilepsy during the chronic phase. On the other hand, in the mild group (two cases), seizures during the acute phase were suppressed by intravenous midazolam (MDL) or lidocaine. The duration of the acute phase was shorter (12 and 24 days). Neither MRI abnormalities nor mental deterioration was observed. Epileptic seizures after the convalescent phase were rare. Conclusions: Among the three severe cases, one corresponded well to Awaya's description, and the others appeared to be more severe. The mild group apparently showed less severity. After reviewing the literature, previously reported patients were no less severe than Awaya's original cases. Therefore it is noteworthy that the two milder cases might indicate that this syndrome has a wider clinical spectrum than previously suspected. The pathogenesis of the disorder could not be clarified by this study. However, after judging the focal brain lesions detected on the MRI in one case, the focal encephalitic process and localization‐related epilepsy as its sequela might offer a partial explanation for the pathogenesis of this disorder.