Chapter 8 - Human Herpes Virus 6B in Mesial Temporal Lobe Epilepsy

Abstract

Mesial temporal lobe epilepsy (MTLE) is one of the most frequently occurring epilepsy syndromes and is often associated with hippocampal sclerosis. Nevertheless, many etiological aspects of MTLE are still unresolved. Several findings suggest a possible role of human herpes virus 6B (HHV-6B) infection in the development of MTLE. Analysis of surgically removed biopsy samples from pharmacoresistent MTLE patients has revealed evidence for HHV-6B, particularly in hippocampal tissue. Co-localization of HHV-6B and astrocytic antigens has been repeatedly reported. In addition, altered expression of glutamate transporters in HHV-6B-infected astrocytes may be involved in glutamatergic exitotoxicity. A review of the literature shows increased HHV-6B detection in biopsy samples from MTLE patients with febrile seizures in childhood or a history of encephalitis. Elevated expression of inflammation- associated factors has been found in HHV-6B-positive samples from MTLE patients; however, HHV-6B detection rates vary considerably between studies, which may be explained by differences in patient populations, PCR techniques, and tissue preparation. It is important to note that, whenever virus-specific differentiation between HHV-6A and HHV-6B was performed in biopsy samples from MTLE patients, virtually all studies revealed the presence of HHV-6B but no evidence for HHV-6A infection.