Human Herpesvirus 6 Encephalitis in Immunocompetent and Immunocompromised Hosts

<p><strong>Objective:&nbsp;</strong>The aim of this study was to analyze the clinical, radiologic, and biological features associated with human herpesvirus 6 (HHV-6) encephalitis in immunocompetent and immunocompromised hosts to establish which clinical settings should prompt HHV-6 testing.</p> <p><strong>Methods:&nbsp;</strong>We performed a retrospective research in the virology for all patients who tested positive for HHV-6 DNA in the CSF and/or in blood and separately assessed the number of patients meeting the criteria for HHV-6 encephalitis in the group of immunocompetent and immunocompromised hosts.</p> <p><strong>Results:&nbsp;</strong>Of the 926 patients tested for HHV-6 during the period of interest, 45 met the study criteria.</p> <p>Among immunocompetent hosts (n = 17), HHV-6 encephalitis was diagnosed to 4 infants or children presenting with seizures or mild encephalopathy during primary HHV-6 infection (CSF/blood replication ratio &lt;&lt;1 in all cases).</p> <p>Among immunocompromised hosts (n = 28), HHV-6 encephalitis was diagnosed to 7 adolescents/adults with hematologic conditions presenting with altered mental status (7/7), seizures (3/7), vigilance impairment (3/7), behavioral changes (2/7), hyponatremia (2/7), and anterograde amnesia (1/7). Initial brain MRI was altered only in 2 patients, but 6 of the 7 had a CSF/blood replication ratio &gt;1.</p> <p><strong>Conclusions:&nbsp;</strong>The detection of a CSF/blood replication ratio &gt;1 represented a specific feature of immunocompromised patients with HHV-6 encephalitis and could be of special help to establish a diagnosis of HHV-6 encephalitis in hematopoietic stem cell transplant recipients lacking radiologic evidence of limbic involvement.</p>