Meningoencephalitis in a background of inherited chromosomic integration of HHV-6 and CMV infection in an immunocompetent adult, which one is the culprit?

HHV-6 meningoencephalitis has been reported in immunocompromised individuals but is very uncommon in immunocompetent individuals. However, HHV-6 is the second most frequently detected virus in multiplex PCR tests. As HHV-6 DNA integrates in the telomeric region of host chromosomes after primary infection and can be passed onto offspring, 1 % of the population carries an inherited HHV-6 genome (iciHHV-6). This makes it difficult to interpret a positive multiplex PCR test for HHV-6. Here, we describe a 39-year-old female patient with an unremarkable medical history and who was hospitalized for meningoencephalitis. The brain imaging findings were normal. The positive multiplex PCR test for HHV-6 was confirmed by qualitative and quantitative HHV-6 PCR tests, the viral load was higher in blood than in CSF. The presence of circulating anti-CMV IgM and IgG in a serologic test and the absence of other pathogens argued in favor of a primary CMV infection. However CMV PCR was negative. The chromosomal integration of HHV-6 was subsequently confirmed by the results of a hair bulb analysis. Our primary hypothesis was CMV meningoencephalitis in a context of inherited chromosomic integration of HHV-6 without be able to confirm the possible role of HHV-6 (reactivation or bystander) in this situation. A commercially available assay able to certify HHV-6 replication in a context of iciHHV-6 would have been useful to conclude.