Herpes simplex virus (HSV) encephalitis represents the most common cause of sporadic viral encephalitis worldwide. This condition is characterized by inflammation and swelling of the brain, leading to serious neurocognitive impairments, particularly in verbal memory. Despite the introduction of antiviral therapy with aciclovir, mortality remains between 5.5% and 12%, and long-term cognitive deficits persist in a significant proportion of patients. Given this, there has been growing interest in adjunctive therapies, particularly corticosteroids, to reduce inflammation and improve outcomes. The DexEnceph trial, a multicentre, observer-blind, phase 3 study conducted across 53 hospitals in the United Kingdom, provides essential insights into the safety and efficacy of dexamethasone as an adjunct therapy for HSV encephalitis.
HSV encephalitis predominantly affects the temporal lobes, which are critical for memory and language processing. This localization contributes to the high incidence of verbal memory deficits observed in patients following infection. In addition to the direct cytopathic effects of the virus, evidence suggests that immune-mediated inflammation contributes significantly to neuronal damage. Elevated levels of inflammatory cytokines such as interleukin-1, interleukin-6, interferon gamma, and monocyte chemotactic protein-1 in cerebrospinal fluid correlate with worse clinical outcomes.
The standard of care remains intravenous aciclovir administered for a minimum of 14 days. While aciclovir effectively reduces viral replication, it does not directly mitigate the host immune response, which can exacerbate brain injury. Corticosteroids, including dexamethasone, have potent anti-inflammatory effects and are used in other central nervous system infections such as bacterial meningitis and tuberculous meningitis. They are also central to treatment in autoimmune encephalitis. However, their role in HSV encephalitis has remained uncertain, with concerns that immune suppression could exacerbate viral replication.
The DexEnceph trial enrolled adults aged 16 years or older with suspected HSV encephalitis confirmed by PCR testing of cerebrospinal fluid. Participants were randomly assigned to receive either intravenous dexamethasone (10 mg four times daily for 4 days) plus aciclovir or aciclovir alone. The primary outcome was verbal memory at 26 weeks, assessed using the Auditory Memory Index of the Wechsler Memory Scale-IV. Secondary outcomes included other cognitive domains, functional measures, neuroimaging parameters, and safety assessments.
Randomization employed a minimization algorithm accounting for age, initial steroid use, Glasgow Coma Scale score at admission, and delay in aciclovir treatment. Outcome assessors, including neuropsychologists and radiologists, were blinded to treatment allocation to reduce bias. Adverse events were carefully monitored and categorized according to severity and relevance to the study intervention.
Between 2016 and 2022, 94 patients were enrolled, with 47 in each treatment group. Modified intention-to-treat analysis included 81 participants. Dexamethasone administration began a median of 7 days after hospital admission. Baseline characteristics, including age, sex, symptoms at presentation, and initial Glasgow Coma Scale scores, were comparable between groups.
The primary outcome showed no significant difference in verbal memory between the dexamethasone and control groups at 26 weeks. The mean verbal memory score was 71 in the dexamethasone group and 69 in the control group. Secondary cognitive assessments, functional outcomes, quality of life measures, and neuroimaging results also demonstrated no significant differences. Importantly, dexamethasone did not increase HSV detection in cerebrospinal fluid at 2 weeks, addressing concerns regarding uncontrolled viral replication.
Safety profiles were similar between groups. Notable adverse events occurred in 40% of patients receiving dexamethasone and 38% of controls. Serious adverse events, such as seizures or thrombotic complications, were rare and evenly distributed. No treatment-related deaths were reported, supporting the safety of dexamethasone in this patient population.
Exploratory post-hoc analysis indicated that earlier administration of dexamethasone in the treatment group was associated with a trend toward improved verbal memory outcomes. Although this observation should be interpreted cautiously due to potential confounding factors and small sample size, it aligns with prior retrospective studies suggesting a benefit when corticosteroids are administered within the first few days of HSV encephalitis onset. This finding highlights the importance of timing in immunomodulatory therapy.
Prior retrospective analyses suggested corticosteroid use might improve outcomes in HSV encephalitis, although these studies were limited by small sample sizes and potential selection bias. The GACHE trial in Germany, which enrolled 41 patients, was prematurely terminated due to slow recruitment, leaving inconclusive evidence. The DexEnceph trial, with 94 participants, represents the most comprehensive randomized assessment of corticosteroids in HSV encephalitis to date.
Unlike the GACHE trial, DexEnceph focused on verbal memory as the primary endpoint, providing a measure directly relevant to the sequelae of temporal lobe involvement. Functional outcomes, quality of life, and imaging metrics served as important secondary endpoints, reinforcing the robustness of the study.
While dexamethasone did not demonstrate efficacy in improving verbal memory or other clinical outcomes, its safety profile suggests potential utility in patients with suspected encephalitis where autoimmune etiology cannot be excluded. Current clinical practice typically delays corticosteroid administration until HSV infection is ruled out, but DexEnceph findings indicate early corticosteroid therapy is unlikely to cause harm.
Corticosteroids remain a mainstay in the treatment of autoimmune encephalitis and other inflammatory CNS conditions. The ability to administer them safely in suspected HSV encephalitis opens avenues for empirical therapy while awaiting definitive diagnostic results, particularly in cases where rapid neuroinflammation may jeopardize patient outcomes.
The DexEnceph trial underscores the need for targeted immunomodulatory strategies rather than broad corticosteroid use. Future research could focus on selective modulation of specific cytokine pathways implicated in neuronal injury, which may provide more effective protection against cognitive deficits. Investigating biomarkers to identify patients most likely to benefit from immunomodulation, including NMDAR antibody status, may enhance individualized therapy.
Additionally, larger multicenter studies with earlier initiation of corticosteroids and diverse patient populations could further clarify whether a specific subgroup derives measurable benefit. The use of advanced neuroimaging and cognitive assessments will continue to be critical in evaluating therapeutic efficacy in HSV encephalitis.
The DexEnceph trial demonstrates that adjunctive dexamethasone is safe in adults with HSV encephalitis but does not improve verbal memory or other functional outcomes compared with standard aciclovir therapy. Early administration may be associated with trends toward improved outcomes, but these findings require cautious interpretation. While routine use of corticosteroids for HSV encephalitis cannot be recommended based on current evidence, their safety supports potential early empirical use in suspected cases of encephalitis before the causative agent is determined. The trial highlights the importance of developing targeted immunomodulatory therapies to minimize inflammation-mediated neuronal injury and improve long-term cognitive outcomes.
Source: Solomon T, Hooper C, Easton A, Rosala-Hallas A, Facer B, Moore P, et al. Safety and efficacy of adjunct dexamethasone in adults with herpes simplex virus encephalitis in the UK (DexEnceph): a multicentre, observer-blind, randomised, phase 3, controlled trial. Lancet Neurol. 2026;25(2):136-146.
Disclaimer: This article is intended for informational purposes and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare provider with any questions regarding medical conditions or treatment options.
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