Clinical characteristic and outcome of HHV-6 encephalitis after allogeneic hematopoietic cell transplantation: A study of Infectious Disease Working Party of EBMT.

Human herpes virus-6 (HHV-6) is the main cause of viral encephalitis in patients undergoing allogeneic hematopoietic cell transplantation (allo-HCT). From January 2005 to December 2014, 97 patients with HHV-6 encephalitis were reported in the EBMT registry. The incidence was 0.45% after the first allo-HCT and varied with the type of donor and of stem cell source: sibling donor 0.06%, unrelated donor 0.68%, haploidentical donor 0.51%, cord blood 2.14%, bone marrow 0.20%, peripheral blood 0.44%. HHV-6 encephalitis occurred at a median time of 31 days from allo-HCT (range 16-317 days). With a median follow-up of 5.28 years, the 5-yr OS was 24.7%. The causes of death were: disease relapse/progression 11, infection 23, non-infectious cause 33, not specified 5. Forty-four deaths (61.1%) occurred within 90 days from diagnosis of HHV-6 encephalitis and in 24 HHV-6 encephalitis was considered a contributory cause. Eight-seven patients received treatment mainly with foscarnet or ganciclovir. In multivariate analysis, bone marrow/peripheral blood stem cell source and nonmyeloablative conditioning regimen were significant factors for lower survival. In conclusion, the incidence of HHV-6 encephalitis was low but associated with high mortality irrespective of antiviral treatment. This confirms the need for further research in this setting.