Meningitis

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management

Definition

Meningitis is an inflammation of the meninges (the protective membranes covering the brain and spinal cord), usually caused by infection. It can be bacterial, viral, fungal, or non-infectious in origin.

Aetiology

The cause of meningitis varies depending on the infective agent.

1. Bacterial Meningitis (Medical Emergency):

  • Neonates: group B Streptococcus, E. coli, Listeria monocytogenes.
  • Children: strep pneumoniae, N. meningitidis, Haemophilus influenzae type B.
  • Adults: strept pneumoniae, N. meningitidis.
  • Immunocompromised/Elderly: Listeria monocytogenes.

2. Viral Meningitis (More Common, Milder Course):

  • Enteroviruses (Coxsackievirus, Echovirus).
  • Herpes simplex virus (HSV-2), Varicella zoster virus (VZV).
  • Mumps virus.

3. Fungal and Other Causes:

  • Cryptococcus neoformans: common in immunocompromised patients (e.g., HIV/AIDS).
  • Non-infectious causes: autoimmune diseases, drug-induced meningitis.

Pathophysiology

  • Pathogens invade the cerebrospinal fluid (CSF), triggering an inflammatory response.
  • Inflammation leads to increased blood-brain barrier permeability and cerebral oedema.
  • Raised intracranial pressure (ICP) can result in neurological complications.

Risk factors

  • Close contact with an infected individual (e.g., meningococcal outbreaks).
  • Immunosuppression (HIV, chemotherapy, splenectomy).
  • Head trauma or neurosurgical procedures.
  • Living in crowded settings (e.g., university halls, military barracks).
  • Unvaccinated individuals (e.g., lack of MenB, MenACWY, Hib vaccines).

Signs and symptoms

Meningitis presents with a combination of systemic and neurological symptoms.

Classic Triad:

  • Fever: High grade and persistent.
  • Neck stiffness (nuchal rigidity): resistance to passive neck flexion.
  • Altered mental status: confusion, drowsiness, irritability.

Other Symptoms:

  • Headache: severe and generalised.
  • Photophobia: sensitivity to light.
  • Seizures: more common in bacterial meningitis.
  • Non-blanching petechial rash: suggests meningococcal septicaemia.
  • Signs of raised ICP: nausea, vomiting, bradycardia, hypertension.

Investigations

  • Urgent CT/MRI: before lumbar puncture if raised ICP is suspected.
  • Lumbar puncture (LP): essential for CSF analysis and pathogen identification.
  • CSF findings:
    • Bacterial meningitis: high protein, low glucose, high neutrophils.
    • Viral meningitis: normal glucose, high lymphocytes.
    • Fungal/TB meningitis: high protein, low glucose, high lymphocytes.
  • Blood cultures: to identify bacteraemia.
  • Polymerase chain reaction (PCR): confirms viral causes (HSV, enterovirus).
  • Meningococcal PCR: if bacterial meningitis is suspected.

Management

1. Empirical IV Antibiotics (Start Immediately) follow local guideline see following examples:

  • Adults: IV Ceftriaxone 2g BD (add IV Amoxicillin if Listeria is suspected, e.g., in the elderly).
  • Neonates: IV Cefotaxime + IV Amoxicillin.

2. Adjunctive Therapy:

  • Dexamethasone: reduces inflammation and risk of neurological sequelae.
  • IV fluids: to maintain hydration and perfusion.
  • Seizure control: if seizures occur, use benzodiazepines (lorazepam).

3. Viral Meningitis Management:

  • Supportive care: hydration, analgesia.
  • HSV/VZV suspected: IV Aciclovir 10 mg/kg TDS.

4. Prevention:

  • Vaccination: MenACWY, MenB, Hib, Pneumococcal vaccines.
  • Post exposure prophylaxis: piprofloxacin or Rifampicin for close contacts of meningococcal cases.

5. Monitoring and Follow-Up:

  • Monitor for complications: Hydrocephalus, hearing loss.
  • Repeat LP if no clinical improvement after 48 hours.
  • Long-term follow-up for neurodevelopmental assessment in children.
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