Human herpesvirus 6 and multiple sclerosis: Systemic active infections in patients with early disease

By means of immunohistochemical staining, cells actively infected with huma n herpesvirus 6 (HHV-6) were found in central nervous system tissues from 8 (73%) of 11 patients with definite multiple sclerosis (MS). Interestingly, 17 (90%) of 19 tissue sections showing active demyelination were positive for HHV-6-infected cells compared with only 3 (13%) of 23 tissue sections f ree of active disease (P<.0001). Central nervous system tissues from 2 of 2 8 normal persons and patients with other inflammatory demyelinative disease s were positive for HHV-6-infected cells (P<.0001), and the 2 positive case s were diagnosed as having HHV-6 leukoencephalitis. By use of a rapid cultu re assay, blood samples from 22 (54%) of 41 patients with definite MS were found to contain active HHV-6 infections, compared with 0 of 61 normal cont rols (P<.0001). No significant difference was found between HHV-6 viremia-p ositive and HHV-6 viremia-negative MS patients with respect to type of dise ase (relapsing/remitting or progressive). In contrast, patients with active HHV-6 viremia were significantly younger and had shorter durations of dise ase than did HHV-6 viremia-negative patients.