Human herpesvirus 6 limbic encephalitis after stem cell transplantation

Central nervous system complications are common in stem cell transplant rec ipients, but selective involvement of the medial temporal area is unusual. The 5 patients reported here presented after stem cell transplantation with increased hippocampal T2 signal on magnetic resonance imaging and increase d hippocampal glucose uptake on [F-18]fluorodeoxyglucose-positron emission tomography (FDG-PET) associated with short-term memory loss, insomnia, and temporal lobe electrographic seizure activity. The initial scalp electroenc ephalograms (EEGs) failed to detect seizure activity in these patients, alt hough the memory dysfunction along with the magnetic resonance imaging and FDG-PET findings suggested subcortical seizure activity. However, extended EEG monitoring revealed repetitive temporal lobe electrographic seizure act ivity. Follow-up MRIs in 2 patients and postmortem findings on 1 patient su ggested that hippocampal sclerosis had developed following the clinical syn drome. Cerebrospinal fluid studies revealed the presence of human herpesvir us 6, variant B, DNA in all of 3 patients who had lumbar punctures. Immunoh istochemical staining for the P41 and P101 human herpesvirus 6 protein anti gens showed numerous immunoreactive astrocytes and neurons in the hippocamp us of 1 of the patients who died from other causes. Because of its subtle c linical presentation, this syndrome may be underrecognized, but can be diag nosed with appropriate magnetic resonance imaging techniques, EEG monitorin g, and cerebrospinal fluid viral studies.