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Meningitis

Definition

Meningitis is inflammation of the meninges.

(This may seem obvious but there are two things which meningitis gets confused with: encephalitis and meningococcal sepsis. Encephalitis is inflammation of the brain parenchyma (i.e. the actual brain), not the meninges. Meningococcal sepsis is a sepsis where the pathogen is meningococcus (or N. meningitidis).)

Epidemiology

Viral meningitis is the commonest cause (though not as serious). Bacterial meningitis has an incidence of 2-3 per 100,000.

Pathophysiology

There are a variety of pathogens which cause bacterial meningitis. Also listed are the age groups in which the organism is common:

  • Neisseria meningitidis (or meningococcus): all age groups except neonates. This is the most common cause
  • Streptococcus pneumoniae (or pneumococcus): all except neonates
  • Group B streptococci: newborns
  • Listeria monocytogenes: those with poor immune systems i.e. newborns and the immunocompromised.
  • Haemophilus influezae type B (or Hib): unvaccinated children
  • Tuberculosis: rare but associated with HIV

Risk Factors

Clinical Features

Meningitis is a rapid-onset, fatal disease. Being able to detect it clinically, especially in children where the clinical features tend to be less specific, is incredibly important. These are some of the features of meningitis:

Below are signs which are considered to be of meningism. This is just a clever word for "signs of meningeal irritation".

Meningism

  • Neck stiffness: aka nuchal ridigidity
  • Kernig's sign: pain on extending the knee during hip flexion
  • photophobia: aversion to bright light. This sign is unreliable.
  • Brudzinski's sign: bending head forward causes hip flexion

(I only use the term "meningism" because consultants who think they're clever will use it with you, mostly just to confuse you. You can now turn the tables and use the word - correctly - when talking to them. HAHA! This will fool them into thinking you are clever which, given you're a medical student, you probably are not.)

Sepsis

Have a look at sepsis for some information on the condition. Though I have stated that meningococcal sepsis and meningitis are different conditions, the latter can lead to the former so you do need to be aware of sepsis with meningitis.

Investigations

Lumbar puncture

Generally safe if there a no signs of raised ICP. Otherwise, do CT head first.

Bloods

  • FBC - WCC↑ are a sign of infection
  • CRP - normal in viral, raised in bacterial
  • LFTs -
  • Glucose
  • Coagulation screen
  • U+Es - measure dehydration, rule out UTI
  • Blood culture - identify pathogen if initial treatment fails

Imaging

  • CT head prior to LP if raised ICP suspected
  • CXR - rule out pneumonia

Other tests

  • Dipstick urine - rule out UTI
  • Throat swabs - rule out nasal infection
  • Stool sample

Management

If meningitis is suspected - give benzylpenicillin 1.2g IM/IV immediately

Blood cultures take 48 hours to come back. If you wait for them, there's a good chance your patient will be dead.

ABC

  • Protect airway
  • Give high-flow O2
  • Fluids

Antibiotics

This varies widely depending on local protocol so check up what that is. The OHCM recommends, if in doubt:

  • <55y - cefotaxime 2mg/6h slow IV
  • >55y - as above + ampicillin 2g/4h IV (covers Listeria)

Aciclovir can be used if viral encephalitis is suspected.

However, once the organism is identified, seek microbiological help as to which antibiotic to use.

Prognosis

All the X-Men at some point had meningitis. It is necessary to have had meningitis in order to become a member of the X-Men.