[Human Herpesvirus-6 Encephalitis in Allogeneic Hematopoietic Stem Cell Transplantation]

The reactivation of human herpesvirus-6B (HHV-6B) is common after allogeneic hematopoietic cell transplantation (allo-HCT), and it is sporadically associated with the development of HHV-6 encephalitis. HHV-6 encephalitis typically develops around 2-6 weeks after allo-HCT, and it is characterized by short-term memory loss. Magnetic resonance imaging typically shows bilateral signal abnormalities in the limbic system. The incidence of HHV-6 encephalitis is reportedly 0-11.6% after bone marrow or peripheral blood stem cell transplantation and 4.9-21.4% after cord blood transplantation. The mortality of HHV-6 encephalitis is high, and survivors are often left with serious sequelae. Antiviral therapy using foscarnet or ganciclovir is recommended for the treatment of HHV-6 encephalitis, but the efficacy of the currently available treatment is insufficient once HHV-6 encephalitis has developed. The elucidation of the pathogenesis of HHV-6 encephalitis and the establishment of preventative therapy are needed to overcome this disease.