Core Highlights
The DexEnceph trial provides critical evidence regarding the use of corticosteroids in the management of Herpes Simplex Virus (HSV) encephalitis. The key takeaways from this multicentre, randomised, phase 3 trial include:
- Adjunct dexamethasone did not significantly improve verbal memory scores at 26 weeks compared to aciclovir alone.
- The safety profile of dexamethasone in this population was satisfactory, with no significant difference in serious adverse events between the treatment and control groups.
- The median time to initiate dexamethasone was 7 days after hospital admission, which may have limited its potential impact on early inflammatory damage.
- Early use of corticosteroids in suspected encephalitis appears unlikely to be harmful, supporting their use in cases where other inflammatory aetiologies are suspected alongside HSV.
The Clinical Burden of Herpes Simplex Encephalitis
Herpes simplex virus (HSV) encephalitis remains the most common cause of sporadic fatal encephalitis worldwide. Despite the standard of care—intravenous aciclovir—which has significantly reduced mortality rates, the morbidity associated with the disease remains high. Many survivors are left with profound neurocognitive sequelae, particularly affecting memory, executive function, and personality, due to the virus’s predilection for the temporal lobes and limbic system.
The pathophysiology of HSV encephalitis involves both direct viral-mediated neuronal destruction and a secondary, robust inflammatory response. This host immune response, while intended to clear the virus, often causes collateral damage to brain tissue, characterized by significant oedema and necrosis. For decades, clinicians have debated whether adjunct corticosteroids could mitigate this inflammatory damage and improve long-term outcomes. Until the DexEnceph trial, high-quality, randomized controlled data to guide this practice were lacking.
The DexEnceph Trial: Methodology and Design
The DexEnceph study was a multicentre, observer-blind, randomised, phase 3, controlled trial conducted across 53 hospitals in the United Kingdom. The study aimed to definitively assess the efficacy and safety of adjunct dexamethasone in adults with PCR-confirmed HSV encephalitis.
Patient Population
Eligible participants were adults aged 16 years or older with suspected encephalitis, defined as a febrile illness with new-onset seizures, focal neurological signs, or altered consciousness/cognition. Inclusion required a positive HSV-1 or HSV-2 PCR test in the cerebrospinal fluid (CSF).
Intervention and Comparator
Participants were randomly assigned to one of two groups:
- Dexamethasone Group: Received intravenous dexamethasone (10 mg/kg, four times daily for 4 days) plus standard intravenous aciclovir (10 mg/kg, three times daily for at least 14 days).
- Control Group: Received intravenous aciclovir alone.
Primary and Secondary Endpoints
The primary outcome was the verbal memory score at 26 weeks, measured by the Wechsler Memory Scale (WMS)-IV auditory memory index. This index was chosen due to the specific vulnerability of memory circuits in HSV encephalitis. Secondary outcomes included global neurological recovery (Glasgow Outcome Scale-Extended), quality of life, and safety parameters.
Key Findings and Statistical Analysis
Between 2016 and 2022, 94 patients were recruited (47 to each group). The modified intention-to-treat (mITT) analysis included 81 patients who completed the primary assessment (39 in the dexamethasone group and 42 in the control group).
Primary Outcome: Verbal Memory
The study failed to meet its primary endpoint. At 26 weeks, the mean verbal memory score was 71 (SD 26) in the dexamethasone group compared to 69 (SD 25) in the control group. The adjusted difference was 1.77 (95% CI -9.57 to 13.12; p=0.76), indicating no statistically significant benefit for the addition of dexamethasone in terms of neurocognitive recovery.
Secondary Clinical Outcomes
Secondary measures of disability and quality of life also showed no significant differences between the two study arms. These results suggest that while dexamethasone is widely used in other forms of meningitis and encephalitis, its standard application in HSV encephalitis at the current dosing and timing does not translate into superior functional or cognitive outcomes.
Safety and Tolerability Profile
A major concern regarding the use of corticosteroids in viral encephalitis is the potential for increased viral replication or secondary infections. However, the DexEnceph trial results provide reassurance regarding safety.
Adverse events were reported in 18 (40%) participants in the dexamethasone group and 18 (38%) in the control group. Serious adverse events (SAEs) were infrequent and balanced between groups. Notable SAEs included seizures requiring readmission and thrombotic events (deep vein thrombosis and pulmonary embolism). Crucially, there were no treatment-related deaths, and the use of steroids did not appear to worsen the clinical course of the viral infection.
Clinical Interpretation and Expert Commentary
The lack of efficacy observed in the DexEnceph trial warrants a deep dive into why the intervention did not produce the expected results. One of the most significant factors identified was the timing of administration. In this trial, dexamethasone was initiated at a median of 7 days after hospital admission. In many cases, the peak of inflammatory damage may have already occurred by the time the steroids were started.
In clinical practice, corticosteroids are often administered much earlier in the course of suspected meningitis or encephalitis (frequently alongside the first dose of antibiotics or antivirals). The trial’s findings suggest that while these early doses may not improve outcomes specifically for HSV, they are unlikely to cause harm. This is particularly important because the initial presentation of HSV encephalitis can mimic other conditions, such as pneumococcal meningitis or autoimmune encephalitis, where early steroids are standard or beneficial.
Furthermore, the dose of dexamethasone used—while high—might not have been sufficient to combat the intense, localized inflammation of the temporal lobes, or perhaps the 4-day duration was too short. Some experts suggest that future research should focus on more targeted immunomodulators or biological agents that address specific pathways of neuroinflammation, such as those involving the N-methyl-D-aspartate (NMDA) receptor or specific cytokines.
Conclusion and Future Directions
The DexEnceph trial is a landmark study that brings much-needed clarity to the management of HSV encephalitis. Although it did not demonstrate a cognitive benefit for adjunct dexamethasone, it established a clear safety profile for its use. For clinicians, the trial supports the status quo of focusing on early and aggressive aciclovir therapy while providing a safety net for those who choose to use steroids for cerebral oedema or in cases where the diagnosis remains broad.
Future studies should investigate the role of hyper-early corticosteroid administration and the potential of more sophisticated immunomodulatory strategies. Until then, aciclovir remains the cornerstone of therapy, and the search for interventions that can preserve long-term cognitive function in these patients continues.
Funding and Trial Registration
The DexEnceph trial was funded by the National Institute for Health and Care Research (NIHR). It is registered with the International Standard Randomised Controlled Trial Number Registry (ISRCTN11774734) and EudraCT (EudraCT2016-004835-19).
References
1. Solomon T, Hooper C, Easton A, 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 Feb;25(2):136-146. doi: 10.1016/S1474-4422(25)00454-5.
2. Whitley RJ, Gnann JW. Herpes simplex encephalitis: clinical manifestations, diagnosis, and management. Lancet Infect Dis. 2002;2(9):561-567.
3. Steiner I, Budka H, Chaudhuri A, et al. Viral encephalitis: a review of diagnostic methods and aetiological agents. Lancet Neurol. 2007;6(11):979-990.