Meningitis

Overview – Meningitis

Meningitis is an acute inflammation of the meninges with potentially life-threatening consequences, particularly when bacterial. It is commonly caused by bacterial or viral pathogens and can rapidly progress to cerebral oedema, raised intracranial pressure, and sepsis. Clinical recognition, empirical treatment, and timely CSF analysis are vital for optimal outcomes. This article outlines the causes, classical signs of meningism, diagnostic red flags, and the CSF interpretation framework essential for clinical practice in final-year medicine.

Definition

Inflammation of the meninges (pia, arachnoid, dura mater), usually due to bacterial, viral, or less commonly fungal or mycobacterial infection.

Aetiology

Bacterial (Septic) Meningitis

• Adults: Neisseria meningitides (meningococcus) – vaccine preventable (A & C)
• Children: Haemophilus influenzae – HIB vaccine preventable
• Neonates: Group B Streptococcus, E. coli

Viral (Aseptic) Meningitis

• HSV
• Enteroviruses (e.g. Echo, Coxsackie)
• Influenza
• Mumps
• HIV

Chronic Meningitis

• Miliary tuberculosis

Fungal Meningitis

• Usually in immunocompromised patients

Pathophysiology

• Infection of the meninges → Inflammatory cytokine release → Cerebral oedema
• ↑Intracranial pressure → vomiting, headache, drowsiness
• Meningococcaemia may trigger thrombocytopenia → petechial rash → DIC

Morphology

• Bacterial: Purulent exudate under the meninges
• Viral: No pus
• Engorgement of meningeal vessels

Clinical Features

Meningism (Classic Triad)

1. Neck Stiffness
   • Brudzinski’s sign (neck flexion → hip/knee flexion)
   • Kernig’s sign (hip flexion → painful knee extension)
2. Photophobia
3. Headache

Other Symptoms

• Fever, vomiting
• Nausea, malaise
• Papilloedema (<1%)
• Irritability, poor feeding (infants)
• Altered consciousness (late)

Aetiology-Specific Clues

• Non-blanching maculopapular rash → Neisseria meningitidis
• CSF rhinorrhoea/otorrhoea → Suggests pneumococcus, HiB, or Strep due to basal skull fracture

Investigations

Immediate Actions

• Blood cultures BEFORE antibiotics

Lumbar Puncture (L3-L5) for CSF Analysis

Contraindications (signs of ↑ICP):

• Papilloedema
• Cushing’s response (↑BP, ↓HR, irregular breathing)
• Unreactive pupils

Risk: Coning (brainstem herniation) → potentially fatal

CSF Sample Breakdown

• Tube 1: Serology / PCR
• Tube 2: Biochemistry (protein, glucose)
• Tube 3: Bacteriology (gram stain & culture – most important)

CSF Interpretation

Management

Bacterial Meningitis

Medical emergency – treat on clinical suspicion

1. Blood cultures first
2. Empirical IV antibiotics immediately
   • IV Benzylpenicillin G or IV Ceftriaxone (crosses BBB)
3. Add corticosteroids (e.g. IV dexamethasone) to reduce CNS inflammation
4. Fundoscopy (for papilloedema) before LP
5. Post-exposure prophylaxis for close contacts:
   • Rifampicin, Ceftriaxone, or Ciprofloxacin

Viral Meningitis

• Typically self-limiting
• Supportive care

Complications

Acute

• Encephalitis
• Cerebral infarction
• Brain herniation
• Cerebral oedema
• Waterhouse-Friderichsen syndrome (adrenal infarction, DIC)

Late

• Brain abscess
• Subdural empyema
• Epilepsy
• Leptomeningeal fibrosis → hydrocephalus

Differential Diagnosis

• Encephalitis
• Brain abscess
• Subarachnoid haemorrhage
• Intracranial tumour
• Migraine (with photophobia)
• Acute febrile illness with myalgia (e.g. influenza)

Summary – Meningitis

Meningitis is an urgent neurological condition that presents with meningism, fever, and headache, and can rapidly progress to cerebral oedema, herniation, or death without timely management. Diagnosis relies on clinical suspicion, lumbar puncture, and CSF analysis. Bacterial meningitis requires immediate empirical antibiotics. For a broader context, see our Nervous System Overview page.