Dexamethasone in Herpes Simplex Virus Encephalitis

Inclusion Criteria: \- Suspected encephalitis criteria: Acute or subacute (up to 4 weeks) alteration in consciousness, cognition, personality or behaviour\* persisting for \> 24 hours Laboratory confirmed HSV by positive PCR on CSF sample. * Receiving intravenous aciclovir dosed at 10mg/kg TDS or at a reduced dose in renal impairment * Age ≥ 18 years * Person affiliated to social security * Written informed consent has been given by the patient or their legal representative Exclusion Criteria: * Currently receiving oral or injectable corticosteroid therapy; including treatment with oral or injectable corticosteroids in the last 30 days. * History of hypersensitivity to corticosteroids * Immunosuppression secondary to: * Known HIV infection \& CD4 count under 200cell/mm3 * Biologic therapy or other immunosuppressive agents \[azathioprine, methotrexate, ciclosporin\] * Solid organ transplant on immunosuppression * Bone marrow transplant * Currently undergoing a course of chemotherapy or radiotherapy * Known immunodeficiency syndrome \[other than HIV\] * Known haematological malignancy * Pre-existing indwelling ventricular devices * Peptic ulcer disease in the last 6 months: defined as a peptic ulcer seen at previous endoscopy or an upper gastrointestinal bleed causing ≥ 2 unit haemoglobin drop * Currently on an antiretroviral regime containing rilpivirine * Patients under legal protection, administrative or judicial control * Pregnancy / Breast feeding and pa…