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Monday, August 11, 2025

Meningitis


Definition
Meningitis is an acute or chronic inflammation of the meninges, the protective membranes covering the brain and spinal cord. It can be caused by bacterial, viral, fungal, or other infectious and non-infectious agents. The condition is a medical emergency due to the risk of severe neurological complications and death if untreated.

Types of Meningitis

1. Bacterial Meningitis – Severe, potentially life-threatening. Common pathogens vary by age group:

  • Neonates: Group B Streptococcus (Streptococcus agalactiae), Escherichia coli, Listeria monocytogenes.

  • Children and adults: Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae type b.

  • Older adults/immunocompromised: S. pneumoniae, L. monocytogenes, Gram-negative bacilli.

2. Viral Meningitis – Generally milder; most often caused by enteroviruses (e.g., echovirus, coxsackievirus), herpes simplex virus type 2 (HSV-2), varicella-zoster virus, and mumps virus.

3. Fungal Meningitis – Usually in immunocompromised patients; common pathogens include Cryptococcus neoformans, Histoplasma capsulatum, and Coccidioides immitis.

4. Parasitic and Non-infectious Meningitis – Rare; caused by certain parasites, drug-induced hypersensitivity, or autoimmune disorders.

Pathophysiology

Infectious meningitis results from pathogen invasion of the central nervous system (CNS), leading to inflammation, increased permeability of the blood–brain barrier, cerebral oedema, and increased intracranial pressure. This can cause neuronal injury due to both direct toxic effects and secondary ischemia.

Risk Factors

  • Age extremes (infants, elderly).

  • Crowded living conditions (military barracks, student dormitories).

  • Immunosuppression (HIV, chemotherapy, corticosteroids).

  • Asplenia.

  • Skull fracture or neurosurgical procedures.

  • Certain geographic regions with higher endemic rates of meningococcal disease.

Clinical Features

Classic Triad (seen in bacterial meningitis)

  • Fever.

  • Neck stiffness (nuchal rigidity).

  • Altered mental status.

Other Common Symptoms

  • Severe headache.

  • Photophobia.

  • Nausea and vomiting.

  • Seizures.

  • Rash (petechial or purpuric in meningococcal meningitis).

Signs

  • Positive Kernig’s sign and Brudzinski’s sign (limited sensitivity).

  • Hypotension and shock in severe cases.

Diagnosis

Urgent Steps

  • Stabilise airway, breathing, circulation.

  • Obtain blood cultures before starting antibiotics.

Investigations

  • Lumbar puncture (LP): Gold standard for diagnosis.

    • Bacterial meningitis: high WBC (predominantly neutrophils), high protein, low glucose, elevated opening pressure.

    • Viral meningitis: lymphocyte predominance, normal or slightly elevated protein, normal glucose.

  • CSF Gram stain and culture: To identify bacteria.

  • Polymerase chain reaction (PCR): For viral detection.

  • CT scan of head before LP if raised intracranial pressure or focal neurological signs suspected.

Management

General Principles

  • Bacterial meningitis is a medical emergency – initiate empirical antibiotics immediately after blood cultures, without waiting for LP results if critically ill.

  • Supportive care: oxygen, IV fluids, management of raised intracranial pressure, seizure control.

Empirical Antibiotic Treatment (Adults)

(Doses given are typical for bacterial meningitis; may vary by region/protocol)

  • Age 18–50 years:

    • Ceftriaxone 2 g IV every 12 hours

    • Plus Vancomycin 15–20 mg/kg IV every 8–12 hours (to cover resistant S. pneumoniae)

  • Age >50 years or immunocompromised:

    • Ceftriaxone 2 g IV every 12 hours

    • Plus Vancomycin as above

    • Plus Ampicillin 2 g IV every 4 hours (to cover L. monocytogenes)

  • Severe penicillin/cephalosporin allergy:

    • Moxifloxacin 400 mg IV daily

    • Plus Vancomycin as above

    • Plus Trimethoprim-sulfamethoxazole (TMP 5 mg/kg IV every 6–8 hours) for Listeria coverage

Adjunctive Therapy

  • Dexamethasone 10 mg IV every 6 hours for 4 days, ideally before or with first antibiotic dose (especially for S. pneumoniae meningitis).

Viral Meningitis

  • Usually supportive care: fluids, analgesics, antipyretics.

  • Acyclovir 10 mg/kg IV every 8 hours for HSV or VZV meningitis.

Fungal Meningitis

  • Cryptococcal meningitis:

    • Amphotericin B (liposomal) 3–4 mg/kg IV daily

    • Plus Flucytosine 25 mg/kg orally every 6 hours for 2 weeks, followed by Fluconazole 400–800 mg daily for consolidation.

Prevention

  • Vaccination:

    • Meningococcal conjugate vaccines (MenACWY, MenB).

    • Pneumococcal vaccines (PCV13, PPSV23).

    • Haemophilus influenzae type b (Hib) vaccine.

  • Prophylaxis for close contacts of meningococcal meningitis:

    • Rifampicin 600 mg orally every 12 hours for 2 days, or

    • Ciprofloxacin 500 mg orally single dose, or

    • Ceftriaxone 250 mg IM single dose.

Complications

  • Hearing loss.

  • Seizures.

  • Hydrocephalus.

  • Cognitive impairment.

  • Death (mortality up to 20% in bacterial meningitis).




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