A case report of anti-N-methyl-d-aspartate receptor encephalitis with chromosomally integrated human herpesvirus 6

Chromosomally integrated human herpesvirus 6 (ciHHV6) is a condition where HHV6-DNA is integrated into the host germline genome. ciHHV6 can be misdiagnosed as active HHV6 infection. We report a 30-year-old woman presenting with psychological symptoms without a history of immunodeficiency. She had an ovarian teratoma and anti-N-methyl-D-aspartate receptor (NMDAR) antibodies in the cerebrospinal fluid (CSF) with HHV6-DNA in the serum and CSF. The final diagnosis was anti-NMDAR encephalitis and ciHHV6 because laparoscopic oophorectomy and immunotherapy ameliorated her symptoms and HHV6-DNA was detected in her oral mucosa cells. This case suggests the need to assess whether HHV6-DNA is related to infection or ciHHV6 when HHV6-DNA is detected in the CSF of patients with encephalitis.