Human herpesvirus 6 meningoencephalitis in allogeneic hematopoietic stem cell transplant recipients.

We retrospectively investigated the clinical characteristics of human herpesvirus 6 (HHV-6) meningoencephalitis within 100 days after allogeneic hematopoietic stem cell transplantation (HSCT). Of 1148 patients who received transplants between January 1999 and December 2003, 11 patients (0.96%) with HHV-6 meningoencephalitis were identified. Ten of 11 recipients received hematopoietic stem cells from donors other than HLA-identical siblings. Confusion was the most frequent central nervous system (CNS) symptom, and a skin rash with high-grade fever preceded the CNS symptoms in 9 patients. Magnetic resonance imaging of the brain showed an abnormal increased T2 signal in the hypothalamus of 5 patients. Eight patients were treated with ganciclovir, and an improvement of CNS symptoms was obtained in 3 patients; 3 patients treated with acyclovir showed no improvement. Improvement in the meningoencephalitis seemed less frequent in patients with abnormal findings in the hypothalamus than in those without such findings. Because the symptoms of HHV-6 meningoencephalitis mimicked those of cyclosporine- or tacrolimus-induced encephalopathy, the drugs were withdrawn at the onset of CNS symptoms in 10 patients, resulting in the development of grade IV graft-versus-host disease (GVHD) in 5 patients. Three patients died of HHV-6 meningoencephalitis, and 6 died of other causes, including GVHD. In conclusion, HHV-6 meningoencephalitis is a rare but potentially life-threatening complication in patients who undergo allogeneic HSCT. Careful assessment of the clinical findings and the brain may allow early and precise diagnosis of HHV-6 meningoencephalitis and contribute to improving its prognosis.