Epileptic Encephalopathy After Human Herpes Virus 6-Related Post-Transplant Acute Limbic Encephalitis in Children: A Case Report and Review of the Literature.

Post-transplant human herpes virus 6 (HHV6) encephalitis can be followed by refractory epilepsy accompanied by intellectual decline after several months. However, such cases are extremely rare, and the disease mechanism remains elusive. We present the case of an eight-year-old boy who presented with epileptic encephalopathy 11 months after developing post-transplant acute limbic encephalitis (PALE) caused by HHV6. The patient developed multiple types of seizures, primarily characterized by epileptic spasms. Significant electroencephalographic (EEG) abnormalities were noted during the interictal period, along with regression of cognitive and language functions and progressive atrophy of the entire brain, including the hippocampus. He was managed with multiple antiepileptic drugs, although his seizures remained uncontrolled for one year after epilepsy onset. Herein, we summarized and analyzed the clinical features of the previously reported cases and the present case. The median time from the onset of HHV6 PALE to epilepsy was 11.5 months. Developmental regression or cognitive decline, multiple seizure types including tonic seizures, generalized slow waves, multifocal spike-wave activity on interictal EEG, brain changes such as hippocampal sclerosis, and poor seizure prognosis are common features. The disease was classified as epileptic encephalopathy following HHV6-related PALE (EE-PALE). This case not only provides additional evidence that EE-PALE is a distinct disease with consistent clinical features but is also expected to contribute to the identification of its pathogenesis and effective treatment.