[Human herpesvirus-6B encephalitis following allogeneic hematopoietic stem cell transplantation: how should it be...

Human herpesvirus (HHV)-6B encephalitis has been increasingly recognized as an important central nervous system (CNS) complication after allogeneic hematopoietic stem cell transplantation. In this review, the best way to diagnose and treat this devastating complication is described. Diagnostic pitfalls: HHV-6B encephalitis should be diagnosed based on the presence of CNS symptoms, positive results for HHV-6 DNA in the cerebrospinal fluid (CSF), and exclusion of other causes of CNS symptoms. There are potential pitfalls when diagnosing HHV-6B encephalitis. Moreover, false-positive detection of HHV-6 DNA in the CSF can occur. Pleocytosis is observed in few patients, and CSF protein levels are often normal. Limbic encephalitis findings are not commonly detected through a brain MRI at the time of development. Prevention: Neither routine monitoring nor routine prophylactic antiviral therapy is recommended to prevent the development of HHV-6B encephalitis. Treatment: Empiric therapy should be started immediately after HHV-6B encephalitis is suspected. The Guideline Committee of the JSHCT recommends full-dose foscarnet (180 mg/kg/day) for the treatment of HHV-6B encephalitis. Therapeutic effect of anti-HHV6 therapy is assessed based on CNS symptoms and HHV-6 DNA in the CSF, which should be evaluated 1-2 weeks after initiating treatment. Even in patients exhibiting good therapeutic effects, antiviral treatment should be continued for at least 3 weeks.