Risk factors of human herpesvirus 6 encephalitis/myelitis after allogeneic hematopoietic stem cell transplantation.

Background: Human herpesvirus 6 (HHV-6) encephalitis/myelitis is now a well-known complication after allogeneic stem cell transplantation (allo-HSCT), particularly after cord blood transplantation (CBT). In this study, we evaluated the risk factors of HHV-6 encephalitis/myelitis.

Methods: We evaluated 253 patients who received allo-HSCT from 2007 to 2015 at our institute. HHV-6 encephalitis/myelitis was defined as HHV-6 DNA detection in the cerebrospinal fluid or peripheral blood by polymerase chain reaction in the presence of typical manifestations without other concurrent condition that led to the manifestations.

Results: HHV-6 encephalitis/myelitis occurred in 11 patients (4.5%) (9 encephalitis, 3.7%; 2 myelitis, 0.8%). Multivariate analysis showed that CBT, mycophenolate mofetil (MMF) for graft-versus-host disease prophylaxis, history of allogeneic hematopoietic stem cell transplantation (allo-HSCT), and engraftment syndrome (ES) were significantly associated with incidence of HHV-6 encephalitis/myelitis (P=.025, P=.017, P=.017, and P=.014, respectively).

Conclusion: Although it has been shown that CBT, ES, and history of allo-HSCT are risk factors for HHV-6 encephalitis/myelitis, our study demonstrated MMF is also a risk factor for the disease.