Encephalitis caused by human herpesvirus-6 in transplant recipients - relevance of a novel neurotropic virus

Background. Human herpesvirus-6 (HHV-6) is a neurotropic virus. Encephalitis is a significant clinical manifestation of HHV-6; however, sparse data on this entity exist in transplant recipients. Methods. Cases of HHV-B encephalitis reported in the literature (13 bone marrow transplant recipients and 1 liver transplant recipient) were reviewed. The diagnosis was established in all by viral isolation and/or detection of HHV-6 DNA in the cerebrospinal fluid by polymerase chain reaction or histopathologic method. Results. HHV-6 encephalitis occurred a median of 45 days (range 10 days to 15 months) after transplantation. Mental status changes, ranging from confusion to coma (92%), seizures (25%), and headache (25%) were the predominant clinical presentations. Focal neurologic findings occurred in only 17% of the patients, Twenty-five percent of the patients had fever; however, the height of fever (less than or equal to 40 degrees C) in febrile patients was striking. Cerebrospinal fluid pleocytosis was generally lacking. Abnormal neuroimaging findings, characterized by low-attenuation lesions in the posterior cerebral lobes, were present only in 17% of the patients. Overall mortality in patients with HHV-6 encephalitis was 58% (7 of 12); 42% (5 of 12) of the deaths were caused by HHV-6. Cure was documented in 7 of 8 patients who received ganciclovir or foscarnet for greater than or equal to 7 days, compared with 0% (0 of 4) in those who did not receive these drugs or received them for < 7 days (P = .01). Conclusions. HHV-6 may be associated with encephalitis after transplantation and warrants consideration in transplant recipients with encephalitis of unidentifiable etiology.