Meningitis

“An infection of the protective membranes that surround the brain and the spinal cord (the meninges)”

Risk Factors

• Extremes of age (<5 or >60)
• Those with a suppressed immune system (e.g. HIV, on immunosuppressants)
• Chronic kidney failure
• Diabetes Mellitus

Aetiology

• Infective
  • Bacterial – e.g. Neisseria meningitides
  • Viral – e.g. Mumps, enteroviruses
  • Fungal – e.g. Cryptococcus neoformans)
• Non-infective (e.g. malignant meningitis)

Pathophysiology

• Microorganisms reach the meninges either by direct (e.g. ears, cranial injury) or bloodstream spread.
  • Acute bacterial: pia-arachnoid congested with polymorphs, resulting in pus formation and adhesions
  • Chronic infection: brain covered in exudate with meningeal tubercles
  • Viral: lymphocytic inflammatory CSF reaction without pus formation, polymorphs or adhesions
• NB cerebral oedema occurs in all bacterial meningitis infections

Clinical Presentation

• Early: headache, leg pains, cold hands and feet, abnormal skin colour
• Later: Meningism (neck stiffness, photophobia, positive Kernig’s sign), decrease in GCS, seizures, petechial rash
• NB: in acute bacterial symptoms more intense and develop within minutes/hours, whereas many viral meningitides have less prominent signs

Investigations

• Bloods:
  • FBC, U+Es, LFT, glucose, coagulation screen
  • Blood cultures
  • Serology
• Imaging:
  • Chest X-Ray – looking for TB signs
  • CT Chest
• Special:
  • Throat swabs, and rectal swab
  • Lumbar puncture: if bacterial appears turbin, polymorphs predominant cell, high cell count/mm³, glucose <1/2 plasma, >1.5g/L protein)

Management

• Minutes save lives and local policies vary
• <55yrs: cefotaxime 2g/6hr slow IV
• >55yrs: cefotaxime + ampicillin (to cover Listeria)
• Viral: Aciclovir

Complications

• Cranial nerve lesions (leading to e.g. hearing loss, blindness)
• Paralysis
• Ataxia
• Recurrent seizures
• Problems with memory and concentration