Overview
Meningitis and Encephalitis
Topic Overview
Summary
Meningitis is inflammation of the meninges; encephalitis is inflammation of the brain parenchyma. They often coexist (meningoencephalitis). Bacterial meningitis is a medical emergency requiring immediate antibiotics. Viral meningitis is usually self-limiting. HSV encephalitis is treatable with aciclovir but rapidly fatal if missed. Classic presentation is fever, headache, neck stiffness (meningism), and altered consciousness (encephalitis). Lumbar puncture is diagnostic but should not delay antibiotics.
Key Facts
- Meningitis triad: Fever + headache + neck stiffness (only 50% have all three)
- Encephalitis: Altered consciousness, behavioural change, seizures
- Bacterial meningitis: Emergency — give antibiotics within 1 hour
- HSV encephalitis: Altered behaviour + temporal lobe signs — give aciclovir empirically
- LP: Diagnostic but DO NOT delay antibiotics if LP delayed
Clinical Pearls
"Don't wait for LP — give antibiotics immediately if bacterial meningitis suspected"
HSV encephalitis: Behavioural change + temporal lobe involvement = aciclovir NOW
Petechial rash + fever = meningococcal disease until proven otherwise
Why This Matters Clinically
Bacterial meningitis and HSV encephalitis are rapidly fatal without treatment. Every hour of delay increases mortality. A high index of suspicion and immediate treatment saves lives.
Visual Summary
Visual assets to be added:
- Meningitis vs encephalitis comparison
- Petechial rash images
- CSF interpretation table
- Empirical antibiotic algorithm
Epidemiology
Meningitis
- Bacterial: 1-2 per 100,000/year (decreased with vaccines)
- Viral: More common (5-10 per 100,000/year)
Encephalitis
- 5-10 per 100,000/year
- HSV is most common sporadic cause
Demographics
- All ages
- Extremes of age: Higher risk
- Immunocompromised: Atypical organisms
Causes
Bacterial Meningitis:
| Age Group | Common Organisms |
|---|---|
| Neonates | Group B Strep, E. coli, Listeria |
| Infants/children | N. meningitidis, S. pneumoniae, H. influenzae |
| Adults | S. pneumoniae, N. meningitidis |
| Elderly/immunocompromised | S. pneumoniae, Listeria, Gram-negatives |
Viral Meningitis:
- Enteroviruses (most common)
- HSV-2
- VZV, mumps, HIV
Encephalitis:
- HSV-1 (most common sporadic)
- VZV, CMV, EBV
- Arboviruses (travel history)
- Autoimmune (anti-NMDAR)
Pathophysiology
Meningitis
- Pathogen enters CSF (haematogenous, direct spread, trauma)
- Bacterial multiplication in CSF
- Inflammatory response → cytokine release
- Cerebral oedema, increased ICP
- Vasculitis → infarction
Encephalitis
- Viral invasion of brain parenchyma
- Direct neuronal damage
- Inflammatory response
- Oedema, necrosis
HSV Encephalitis
- HSV-1 reactivation or primary infection
- Predilection for temporal lobes
- Haemorrhagic necrosis
Clinical Presentation
Meningitis Symptoms
Encephalitis Symptoms
Signs
| Sign | Description |
|---|---|
| Kernig's sign | Resistance to knee extension when hip flexed |
| Brudzinski's sign | Neck flexion causes hip flexion |
| Petechial/purpuric rash | Meningococcal (does NOT blanch) |
| Papilloedema | Raised ICP (caution with LP) |
| Focal neurology | Encephalitis, abscess, stroke |
Red Flags
| Finding | Significance |
|---|---|
| Non-blanching rash | Meningococcal sepsis — give IM benzylpenicillin pre-hospital |
| Reduced GCS | Severe — ICU |
| Seizures | Encephalitis |
| Focal signs | CT before LP; consider abscess |
Headache (severe)
Common presentation.
Fever
Common presentation.
Neck stiffness
Common presentation.
Photophobia
Common presentation.
Nausea, vomiting
Common presentation.
Clinical Examination
General
- Fever
- Rash (non-blanching)
- Altered consciousness
Neurological
- Meningism (neck stiffness)
- Kernig's, Brudzinski's signs
- GCS
- Focal signs
- Fundoscopy (papilloedema)
Investigations
Blood Tests
| Test | Purpose |
|---|---|
| FBC | WCC, platelets |
| CRP, procalcitonin | Inflammation (procalcitonin higher in bacterial) |
| U&E, glucose | Baseline, CSF comparison |
| Coagulation | Before LP |
| Blood cultures | Essential — before antibiotics if possible |
| Lactate | Sepsis |
Lumbar Puncture — Key Investigation
CSF Analysis:
| Parameter | Bacterial | Viral | HSV Encephalitis |
|---|---|---|---|
| Appearance | Turbid | Clear | Clear or blood-stained |
| WCC | High (neutrophils) | Moderate (lymphocytes) | Lymphocytes |
| Protein | High | Normal/mildly raised | Raised |
| Glucose | Low (under 40% plasma) | Normal | Low/normal |
| Gram stain | May show organism | Negative | Negative |
| PCR | Bacterial PCR | Enterovirus PCR | HSV PCR (diagnostic) |
Contraindications to LP:
- Reduced GCS (under 13)
- Focal neurology
- Papilloedema
- Coagulopathy
- Haemodynamic instability
- Seizures
→ CT head before LP if contraindications present; DO NOT delay antibiotics
Imaging
| Modality | Indication |
|---|---|
| CT head | Before LP if contraindications; if focal signs |
| MRI brain | Encephalitis (temporal lobe changes in HSV) |
Classification & Staging
By Aetiology
- Bacterial
- Viral
- Fungal (immunocompromised)
- TB
By Anatomy
- Meningitis (meninges)
- Encephalitis (brain parenchyma)
- Meningoencephalitis (both)
Management
Bacterial Meningitis — EMERGENCY
Antibiotics — Give Within 1 Hour:
| Setting | Regimen |
|---|---|
| Community-acquired (adults) | Ceftriaxone 2g IV BD + dexamethasone |
| If Listeria risk (over 60, immunocompromised) | Add amoxicillin 2g IV 4-hourly |
| Pre-hospital (if rash) | IM benzylpenicillin |
Dexamethasone:
- 0.15 mg/kg IV QDS for 4 days
- Give with or just before first antibiotic dose
- Reduces mortality and hearing loss (pneumococcal)
HSV Encephalitis
| Treatment | Details |
|---|---|
| Aciclovir | 10 mg/kg IV TDS for 14-21 days |
| Start empirically | If encephalitis suspected |
| Do NOT wait for PCR |
Viral Meningitis
- Usually self-limiting
- Supportive care
- Analgesia, antiemetics
Supportive Care
- IV fluids (avoid over-hydration — cerebral oedema)
- Seizure management
- ICU if GCS under 8 or haemodynamically unstable
Public Health
- Notify meningococcal disease
- Chemoprophylaxis for close contacts (ciprofloxacin or rifampicin)
Complications
Acute
- Cerebral oedema
- Seizures
- Stroke (vasculitis)
- DIC (meningococcal)
- Death
Long-Term
- Hearing loss (especially pneumococcal)
- Cognitive impairment
- Epilepsy
- Focal neurological deficits
Prognosis & Outcomes
Bacterial Meningitis
- Mortality: 10-30%
- Morbidity: 20-30% have sequelae
HSV Encephalitis
- Mortality without treatment: 70%
- With treatment: 20-30%
- Many survivors have neurological sequelae
Viral Meningitis
- Excellent prognosis
- Full recovery typical
Evidence & Guidelines
Key Guidelines
- NICE CG102: Bacterial Meningitis and Meningococcal Disease
- British Infection Association Guideline on Encephalitis
Key Evidence
- Dexamethasone reduces mortality in pneumococcal meningitis
- Early antibiotics improve survival
Patient & Family Information
What is Meningitis/Encephalitis?
Meningitis is infection of the lining of the brain. Encephalitis is infection of the brain itself. Both are serious and need urgent treatment.
Symptoms
- Severe headache
- Fever
- Stiff neck
- Rash that doesn't fade (meningococcal)
- Confusion or drowsiness
When to Seek Help
- Call 999 immediately for rash, drowsiness, or severe symptoms
Treatment
- Antibiotics (bacterial meningitis)
- Antiviral (HSV encephalitis)
- Hospital admission
Resources
References
Primary Guidelines
- NICE. Bacterial Meningitis and Meningococcal Septicaemia (CG102). 2010 (updated 2015). nice.org.uk
- McGill F, et al. The UK joint specialist societies guideline on the diagnosis and management of acute meningitis and meningococcal sepsis in immunocompetent adults. J Infect. 2016;72(4):405-438. PMID: 26845731
Key Reviews
- van de Beek D, et al. Advances in treatment of bacterial meningitis. Lancet. 2012;380(9854):1693-1702. PMID: 23141618