A case of opsoclonus-myoclonus syndrome with the presence of chromosomally integrated human herpes-virus 6B

A 63-year-old man presented with balance difficulties and vision abnormalities. Continuous conjugate eye oscillations in horizontal and rotary direction and head tremor were observed, all of which indicated opsoclonus-myoclonus syndrome (OMS). Brain MRI was normal. A lumbar puncture revealed mild pleocytosis and elevated proteins. Several neurotropic virus genomes, including Herpes Simplex Virus 1-2, Varicella Zoster Virus, Epstein Barr Virus, Human Cytomegalovirus, Human Herpes Virus 6 A and B, HIV, JC PolyomaVirus, West Nile Virus, flebovirus and entreoviruses, were searched in the cerebrospinal fluid (CSF) and in the blood. Only Human Herpesvirus 6 (HHV6) DNA was detected in both the tested clinical specimens, with a load of 3.0 x 103 copies/mL and 9.8 x 106 in the CSF and blood, respectively. Additionally, HHV6 DNA was detected in the plasma (2.5 x 106 copies/mL). HHV-6 positive samples also molecularly characterized as HHV6B (HST strain). Ganciclovir (5 mg/kg every 12h) was given to the patient for two weeks and a complete recovery was observed. Following the therapy administration, peripheral blood and serum were periodically collected in order to monitor the HHV6 replication. The viral load was stable in the PBMCs isolated from the peripheral blood (range 4.2 x 105 copies/mL-5.2 x 106 copies/mL) and slightly decreased in the plasma (range 2.5 x 106 copies/mL- 8.1 x 103 copies/mL). Due to the constant high presence of the virus genome in the clinical specimens, the chromosomal integration of HHV6 (CIHHV6) was investigated, and the viral genome was also found in the hair follicle (467.8 copies/mL). The presence of CIHHV6 made this case exceptionally challenging, since so far many issues still need to be addressed regarding the association of CIHHV6 with clinical manifestations. Particularly, CIHHV6 subjects may reactivate their own strains and/or be more vulnerable to exogenous strains due to tolerance. Thus, having CIHHV6 may be one of the cause of symptomatic exacerbations and does not exclude the possibility that patients need antiviral treatment. Additionally, even if HHV-6B may rarely cause encephalitis in immunocompetent adults, it should be considered in OMS cases.