Meningitis defination,causes , symptoms, medical management
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Meningitis
Definition
Meningitis is an inflammatory process involving the leptomeninges within the subarachnoid space - the membranes (pia and arachnoid mater) surrounding the brain and spinal cord. If the infection extends into the underlying brain parenchyma, it is termed meningoencephalitis.
The term applies in both infectious and non-infectious settings:
- Infectious meningitis - bacterial, viral, fungal, tuberculous
- Chemical meningitis - response to an irritant (e.g., debris from a ruptured epidermoid cyst)
- Carcinomatous meningitis - metastatic cancer cells spreading to the subarachnoid space
Robbins & Kumar Basic Pathology, p. 833
Classification
| Type | Onset | Common Cause |
|---|---|---|
| Acute pyogenic | Hours - days | Bacterial |
| Aseptic | Days | Viral (most common) |
| Chronic | Weeks - months | Tuberculous, fungal, spirochetal |
Causes
Bacterial Meningitis (Acute Pyogenic)
Causative organisms vary strongly by patient age and risk factors:
| Patient Group | Likely Organisms |
|---|---|
| Neonates | Escherichia coli, Group B Streptococci |
| Adolescents & Young Adults | Neisseria meningitidis |
| Adults (all ages) | Streptococcus pneumoniae (most common overall) |
| Age >50, immunocompromised | S. pneumoniae, Listeria monocytogenes |
| Post-neurosurgical / hospital-acquired | Staphylococcus aureus, gram-negative bacilli |
| Sinusitis/Otitis-associated | Polymicrobial, anaerobes |
Bradley & Daroff's Neurology in Clinical Practice, p. 1698
Viral Meningitis (Aseptic)
The most common form overall. Major causes include:
- Enteroviruses (most frequent)
- Herpes Simplex Virus (HSV-1, HSV-2)
- Varicella-Zoster Virus
- HIV (primary infection)
- Mumps, Epstein-Barr Virus
Chronic Meningitis
- Tuberculous (Mycobacterium tuberculosis) - leading cause of chronic meningitis worldwide
- Fungal - Cryptococcus neoformans (especially in immunocompromised patients)
- Spirochetal - Treponema pallidum (neurosyphilis), Borrelia spp. (Lyme disease)
Routes of Entry
- Hematogenous spread - from nasopharyngeal colonization (S. pneumoniae, N. meningitidis) or bacteremia
- Contiguous spread - from sinusitis, otitis media, mastoiditis
- Direct inoculation - trauma, neurosurgical procedures
- Foodborne - Listeria monocytogenes via contaminated food
Symptoms & Clinical Features
Classic Triad
- Fever
- Severe headache
- Nuchal rigidity (neck stiffness)
Additional features include:
- Photophobia (sensitivity to light)
- Phonophobia (sensitivity to sound)
- Altered mental status / clouding of consciousness
- Irritability, malaise
- Nausea and vomiting
- Seizures (in severe or complicated cases)
Special Presentations
| Population | Atypical Features |
|---|---|
| Neonates | Bulging fontanelle, poor feeding, hypotonia, behavioral changes - classic triad often absent |
| Elderly / Immunocompromised | Altered mental status may be the only finding |
| Meningococcal disease | Petechiae and purpuric rash (non-blanching) on extremities; can progress to Waterhouse-Friderichsen syndrome (bilateral adrenal hemorrhage) + DIC |
| Tuberculous meningitis | Subacute/chronic onset over weeks-months; fever, weight loss, night sweats, malaise - sometimes without classic meningismus |
| Fungal meningitis | Subtle presentation even in healthy adults; low-grade fever, headache, weight loss |
Clinical Signs on Examination
- Kernig's sign - inability to extend the knee when the hip is flexed to 90°
- Brudzinski's sign - passive neck flexion causes involuntary hip and knee flexion
- Both have low sensitivity (<12%) but high specificity - if present, they strongly suggest meningitis
- Papilledema - suggests raised intracranial pressure
- Focal neurologic deficits - suggest mass lesion or complication
Rosen's Emergency Medicine, 2272
Diagnosis
Lumbar Puncture (LP) - CSF Analysis
LP is the definitive diagnostic test. It should be performed without delay in patients with no focal neurologic signs, papilledema, or signs of raised ICP. Do not delay antibiotics waiting for LP - antibiotics can sterilize CSF within 1 hour.
| Parameter | Bacterial | Viral | Tuberculous | Fungal |
|---|---|---|---|---|
| Appearance | Turbid/purulent | Clear | Clear/xanthochromic | Clear |
| Opening pressure | Elevated | Normal/mildly elevated | Elevated | Elevated |
| WBC | 100-10,000 (neutrophils) | 10-1,000 (lymphocytes) | 10-500 (lymphocytes) | 10-200 (lymphocytes) |
| Protein | Elevated (100-500 mg/dL) | Normal/mildly elevated | Elevated | Elevated |
| Glucose | Low (<40 mg/dL) | Normal | Low | Low |
Washington Manual of Medical Therapeutics; Bradley & Daroff's Neurology
Other Investigations
- Blood cultures (before antibiotics if possible)
- CT scan - before LP if papilledema, focal deficits, seizures, altered consciousness, or immunocompromised state
- CBC, CRP, procalcitonin - systemic infection markers
- Blood glucose - to compare with CSF glucose
- Meningitis/encephalitis PCR panel (CSF) - identifies multiple pathogens rapidly
Medical Management
1. Empiric Antibiotic Therapy
Antibiotics must be started IMMEDIATELY - delay is associated with death and poor outcomes.
| Patient | Empiric Regimen | Target Organisms |
|---|---|---|
| Immunocompetent adult | Ceftriaxone 2g IV q12h + Vancomycin 15-20 mg/kg IV | S. pneumoniae, N. meningitidis |
| Age >50 years | Ceftriaxone 2g IV q12h + Vancomycin + Ampicillin 2g IV q4h | Add coverage for Listeria |
| Penicillin allergy | Meropenem 2g IV OR Moxifloxacin 400mg IV + Vancomycin | - |
| Post-neurosurgical | Vancomycin + Meropenem/Cefepime | S. aureus, gram-negatives |
| Neonates | Ampicillin + Cefotaxime | E. coli, Group B Strep |
Tintinalli's Emergency Medicine, p. 1215
CNS Antibiotic Dosages (Bradley & Daroff's):
- Vancomycin: 40-60 mg/kg/day divided q8-12h
- Ceftriaxone: 2g q12h
- Ampicillin: 2g q4h
- Cefepime: 2g q8h
- Metronidazole: 500mg q6h
2. Adjunctive Corticosteroids
Dexamethasone 10 mg IV every 6 hours for 4 days - given before or with the first dose of antibiotics.
- Reduces CSF inflammation, meningeal swelling
- Significantly reduces mortality and morbidity, especially in pneumococcal meningitis
- Reduces hearing loss and neurologic sequelae in children
- Can be given up to 4 hours after antibiotic initiation if not given beforehand
- Concern that dexamethasone reduces CSF vancomycin penetration has been largely refuted by clinical studies
Bradley & Daroff's Neurology, p. 1700; Tintinalli's, p. 1215
3. Specific Therapy (once organism identified)
| Organism | Definitive Antibiotic |
|---|---|
| S. pneumoniae (penicillin-sensitive) | Penicillin G or Ceftriaxone |
| S. pneumoniae (resistant) | Vancomycin + Ceftriaxone |
| N. meningitidis | Penicillin G or Ceftriaxone |
| Listeria monocytogenes | Ampicillin ± Gentamicin |
| E. coli / Gram-negatives | Ceftriaxone or Meropenem |
| M. tuberculosis | RIPE: Rifampicin + Isoniazid + Pyrazinamide + Ethambutol (2 months), then Rifampicin + Isoniazid (7-10 months) |
| HSV (viral encephalitis/meningitis) | Acyclovir IV |
| Cryptococcus | Amphotericin B + Flucytosine, then Fluconazole |
4. Supportive Management
- Monitor closely for respiratory and neurologic deterioration
- Treat fever with antipyretics
- Seizure management with anticonvulsants (benzodiazepines acutely, levetiracetam or phenytoin for ongoing seizures)
- Fluid management - avoid hypotonic fluids; monitor serum sodium for SIADH or cerebral salt wasting
- ICP management if raised: head of bed at 30°, mannitol, avoid hypercapnia
- Isolation precautions - droplet precautions until N. meningitidis is excluded (for 24 hours after antibiotics)
- Chemoprophylaxis for close contacts of meningococcal meningitis: Rifampicin or Ciprofloxacin
5. Viral Meningitis
- Mostly supportive care (rest, analgesia, hydration)
- Acyclovir IV if HSV meningitis/encephalitis is suspected
- Treatment for Lyme disease, TB, and fungal meningitis as per specific agents above
Complications
- Hearing loss (most common long-term sequela, especially with S. pneumoniae and H. influenzae)
- Hydrocephalus
- Cerebral venous thrombosis (~1% of cases)
- Brain abscess
- Subdural empyema
- Septic shock / DIC
- Waterhouse-Friderichsen syndrome (meningococcal disease)
- Death (untreated bacterial meningitis is nearly uniformly fatal)
Recent Evidence
A 2026 Lancet Infectious Diseases guideline for tuberculous meningitis (PMID: 40840485) provides updated clinical practice recommendations - the most recent comprehensive guideline for TB meningitis management.
Sources:
- Robbins & Kumar Basic Pathology
- Rosen's Emergency Medicine: Concepts and Clinical Practice
- Bradley & Daroff's Neurology in Clinical Practice
- Tintinalli's Emergency Medicine: A Comprehensive Study Guide
- Washington Manual of Medical Therapeutics
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