Herpes encephalitis during natalizumab treatment in multiple sclerosis.

In this case report we describe the first non-fatal herpes simplex virus encephalitis (HSE) case with natalizumab for multiple sclerosis (MS). A 36-year-old woman, previously treated with immunomodulatory and immunosuppressive drugs for MS, developed acute encephalitis after 6 monthly natalizumab perfusions. Brain imaging demonstrated suggestive bi-temporal lesions. Herpes simplex virus type-1 DNA was detected in cerebrospinal fluid. The patient improved gradually after a 21-day course of intravenous acyclovir, but neuropsychiatric changes remained 5 months later. Our non-fatal case of HSE and other reported cases of herpes infections provide evidence of an increased risk with natalizumab and point to the need for clinicians to maintain awareness.