Clinical and imaging findings suggesting human herpesvirus 6 encephalitis.

We sought to distinguish patients testing positive for human herpesvirus 6 from those testing negative, based on clinical features and magnetic resonance images. Sixteen immunosuppresed patients were tested by polymerase chain reaction for human herpes virus 6 DNA in cerebrospinal fluid (nine positive results). Medical records were examined for agitation, altered mental status, hallucinations, insomnia, memory loss, and seizures. Patients were sorted by viral status. Clinical features were compared with imaging findings. Insomnia, agitation, and hallucinations were preferentially evident in human herpes virus 6-positive patients. Imaging abnormalities were evident in the hippocampus of both groups. However, extrahippocampal involvement was more common in human herpes virus 6-positive patients and among those with insomnia and hallucinations or seizures. Patients with memory loss and imaging abnormalities in the entorhinal cortex or amygdala were likely to test positive, as were patients with hallucinations and abnormal magnetic resonance signal in the hippocampus. Human herpes virus 6 encephalitis patients present with diverse clinical features that are also common among patients who test negative. This entity should be suspected in patients who present with insomnia, seizures, or hallucinations when imaging abnormalities are evident in the hippocampus, amygdala, and limbic structures beyond the medial temporal lobe.