Human Herpesvirus 6 Encephalitis in Immunocompetent and Immunocompromised Hosts

Area of Science:

• Neurovirology
• Infectious Diseases
• Clinical Neurology

Background:

• Human herpesvirus 6 (HHV-6) is a common viral infection that can cause encephalitis.
• Distinguishing HHV-6 encephalitis in immunocompetent versus immunocompromised hosts is clinically important.
• Understanding the clinical, radiologic, and biological features aids in timely diagnosis and management.

Purpose of the Study:

• To analyze clinical, radiologic, and biological features of HHV-6 encephalitis.
• To differentiate HHV-6 encephalitis presentation in immunocompetent and immunocompromised hosts.
• To identify clinical settings that warrant HHV-6 testing.

Main Methods:

• Retrospective analysis of patients with HHV-6 DNA in CSF and/or blood (January 2008 - September 2018).
• Categorization of patients into immunocompetent and immunocompromised groups.
• Assessment of clinical symptoms, radiologic findings (MRI), and CSF/blood replication ratios.

Main Results:

• Of 926 tested patients, 45 met criteria for HHV-6 encephalitis.
• In immunocompetent hosts (n=17), encephalitis occurred in infants/children with seizures/mild encephalopathy (CSF/blood ratio <<1).
• In immunocompromised hosts (n=28), encephalitis occurred in adolescents/adults with hematologic conditions, altered mental status, and a CSF/blood ratio >1 in most cases (6/7).

Conclusions:

• A CSF/blood replication ratio >1 is a specific marker for HHV-6 encephalitis in immunocompromised patients.
• This ratio is particularly useful for diagnosing HHV-6 encephalitis in hematopoietic stem cell transplant recipients without clear radiologic signs.
• HHV-6 testing should be considered in specific clinical scenarios, especially in immunocompromised individuals with neurological symptoms.