A comprehensive overview of diagnosis, management, and outcomes for this neurological emergency in intensive care settings
Imagine an invisible enemy army penetrating the most protected fortress of your body: your brain. This is what happens during infectious meningoencephalitis, a simultaneous inflammation of the meninges (brain envelopes) and the brain parenchyma 3 . In non-immunocompromised adults, this condition represents an absolute medical emergency that often requires admission to intensive care. Every hour counts, as inflammation can cause irreversible neurological damage in just a few hours. Thanks to a recent European study including nearly 600 patients, we now better understand the keys to improving survival and reducing sequelae of this formidable disease 1 .
Simultaneous infection of meninges and brain tissue
Rapid progression to irreversible neurological damage
Often requires intensive care management
Our central nervous system is protected by several barriers. The meninges, consisting of the dura mater, arachnoid, and pia mater, envelop the brain like successive protective layers 3 . The subarachnoid space, located between the arachnoid and pia mater, contains the cerebrospinal fluid (CSF) that bathes and nourishes the brain. When an infectious agent - virus, bacterium or other - invades this space, an inflammatory reaction is triggered; this is meningitis. When the infection reaches the brain tissue itself, it is then called meningoencephalitis 3 .
Pathogens reach the brain mainly through the hematogenous route (via the bloodstream), more rarely by contiguity from ENT infections or by direct inoculation during trauma 3 .
In non-immunocompromised adults, meningoencephalitis typically manifests as a combination of three syndromes 3 :
| Infection Type | Pathogens | Frequency | Characteristics |
|---|---|---|---|
| Bacterial Meningitis | Streptococcus pneumoniae (pneumococcus) | 60% of bacterial meningitis | Particularly severe |
| Other bacteria | 40% of bacterial meningitis | Various presentations | |
| Infectious Encephalitis | Herpes virus (HSV) | 35% | Preferential target of the nervous system |
| Mycobacterium tuberculosis | 11% | Often more insidious form | |
| Other viruses (VZV, enteroviruses, etc.) | 54% | Various clinical presentations |
Under the auspices of the European Society of Intensive Care Medicine (ESICM), a prospective observational study was conducted between June 2017 and April 2020 in 68 intensive care units spread across 7 European countries 1 . This research included 589 adult patients in whom a diagnosis of probable or confirmed encephalitis had been retained according to the rigorous criteria of the Infectious Disease Society of America.
The primary objective was to identify prognostic factors at 3 months, assessed according to the modified Rankin scale (a score of 3 to 6 indicating a poor prognosis, with score 6 corresponding to death) 1 . Etiological investigations and management were left to the discretion of the investigators, thus reflecting real clinical practice.
The study revealed that bacterial meningitis accounted for 42% of cases, followed by infectious encephalitis (24%), while a quarter of cases (26%) remained without an identified etiology despite investigations 1 . Pneumococcus dominated among bacteria, while herpes virus (HSV) and Mycobacterium tuberculosis were the main agents of infectious encephalitis.
The overall prognosis was severe: 50.5% of patients had a poor prognosis at 3 months, with a mortality rate of 26% 1 . Multivariate analysis identified specific risk factors according to etiology.
| Type | Factors Associated with Poor Prognosis | Protective Factors |
|---|---|---|
| Bacterial Meningitis | Motor response < 3 (GCS) (OR 2.56), Hemiparesis/hemiplegia (OR 3.53) | 3rd Gen Cephalosporin at Day 1 (OR 0.39) |
| Infectious Encephalitis | Age > 60 years (OR 2.15), Immunosuppression (OR 2.16), ICU delay > 1 day (OR 2.23) | Acyclovir at Day 1 (OR 0.47) |
| Entire Cohort | Age > 60 years, Respiratory and cardiovascular complications | - |
The European study highlighted two modifiable factors that favorably influence the prognosis of infectious encephalitis: the speed of ICU admission and early administration of acyclovir (from the first day) 1 . The latter reduces the risk of poor prognosis by more than 50% (OR 0.47) in encephalitis, mainly those caused by the herpes virus.
Similarly, in bacterial meningitis, the use of a 3rd generation cephalosporin from the first day divides the risk of poor prognosis by more than two (OR 0.39) 1 . These results underline the crucial importance of early and appropriate therapeutic management.
Among non-modifiable factors, advanced age (> 60 years) and the presence of focal neurological signs such as hemiparesis or hemiplegia are associated with a less favorable prognosis 1 . The severity of the initial neurological impairment, measured by the motor response of the Glasgow score, is also predictive of evolution.
Associated with 2.15x increased risk of poor outcome in infectious encephalitis
Hemiparesis/hemiplegia increases risk by 3.53x in bacterial meningitis
Doubles the risk of poor outcome in infectious encephalitis
Motor response < 3 on Glasgow Coma Scale increases risk by 2.56x
When faced with a patient with suggestive signs, the diagnosis of meningoencephalitis rests on several pillars 3 :
Key examination that allows analysis of cerebrospinal fluid and identification of the pathogen
CT or MRI to look for signs of inflammation and cerebral edema
Assess inflammatory syndrome and associated failures
The World Health Organization (WHO) recently published its first global guidelines for the diagnosis, treatment and care of meningitis, aiming to accelerate detection and improve long-term management 5 .
Management combines several aspects 1 :
| Tool/Technique | Function | Importance |
|---|---|---|
| IDSA 2013 Criteria | Standardization of diagnosis | Allows homogeneous identification of cases for research and care |
| Lumbar Puncture | CSF analysis | Identification of pathogen and therapeutic guidance |
| Modified Rankin Scale | Assessment of functional prognosis | Standardized measurement of sequelae at 3 months |
| Intravenous Acyclovir | Antiviral treatment | 53% reduction in risk of poor prognosis in herpes encephalitis |
| 3rd Gen Cephalosporin | First-line antibiotic therapy | 61% reduction in risk of poor prognosis in bacterial meningitis |
Despite advances, the European study raises several challenges. A quarter of severe meningoencephalitis cases remain without etiological diagnosis, a worrying figure in the era of modern molecular biology techniques 1 . Furthermore, the lack of detailed information on specific neuro-intensive care management and incomplete assessment of cognitive and social sequelae limit our understanding of the determinants of long-term prognosis.
The WHO aims to:
25% of cases remain without identified cause despite modern diagnostic techniques
Lack of detailed neuro-ICU management information and long-term cognitive assessment
Need for comprehensive management of sequelae including hearing, cognitive and neurological deficits
Infectious meningoencephalitis in non-immunocompromised adults remains a formidable pathology that often involves vital and functional prognosis. Recent literature data teaches us that every minute counts and that two simple but crucial actions can significantly improve prognosis: early ICU admission allowing specialized management of vital failures, and the rapid initiation of appropriate anti-infective treatment.
Thanks to large multicenter studies and new WHO guidelines, modern medicine has increasingly effective tools to confront this neurological scourge. Continued research on still unknown causes and optimization of neuroprotective strategies foreshadows a future where the dramatic sequelae of this disease could become the exception rather than the rule.