Meningitis
Inflammation of the meninges, most dangerously from bacterial invasion of the normally sterile subarachnoid space, where speed of antibiotic delivery, not diagnostic certainty, determines survival.
In a nutshell
Bacterial invasion of the normally sterile, weakly-defended subarachnoid space allows rapid proliferation and a cytokine-driven inflammatory response causing cerebral oedema. Because deterioration can occur within hours, antibiotics are given immediately on clinical suspicion and never delayed for investigation.
Classic presentation
Sudden-onset fever, severe headache, neck stiffness and photophobia, with a non-blanching purpuric rash pointing specifically to meningococcal disease.
Key points
- The classic triad of fever, neck stiffness and altered mental state is present together in only a minority of cases. Clinical suspicion should not depend on all three.
- Antibiotics are given immediately on suspicion and must never be delayed for lumbar puncture or CT.
- Benzylpenicillin is given pre-hospital when meningococcal disease is suspected in the community.
- Dexamethasone targets the inflammatory cerebral oedema and is given alongside the first dose of antibiotics in bacterial meningitis.
- CT head is only needed first if there are signs suggesting raised intracranial pressure or a mass lesion, and even then should not delay antibiotics.
- Meningococcal disease is notifiable, requiring public health notification and prophylaxis for close contacts.
First-line investigation
Lumbar puncture with CSF analysis, performed once safe to do so, but never before, or instead of, giving antibiotics.
First-line management
Immediate empirical IV antibiotics (with pre-hospital benzylpenicillin if meningococcal disease is suspected) plus dexamethasone alongside the first dose in bacterial meningitis.
Exam traps
- Waiting for a CT head or lumbar puncture before giving antibiotics is a fatal delay. Treat first on clinical suspicion.
- The absence of a rash does not exclude meningococcal disease; the rash is a feature of septicaemia, not meningitis itself.
- A well-looking patient with a normal GCS can still have meningitis: the classic triad is insensitive.
- Contact prophylaxis is for close contacts of meningococcal disease, not for all meningitis regardless of organism.
Educational content pending clinical review. Not medical advice.