Meningitis

Here I’ll run through the differentials to consider, the likely organisms and first line treatments, as well as what to look for when interpreting a lumbar puncture of a patient with suspected meningitis.

Immediate actions

If a patient comes in with a fever and altered mental status, you should be thinking about bacterial meningitis as your biggest concern. So use the sepsis six

Give three

• oxygen
• fluids
• antibiotics
  • IV ceftriaxone – broad spectrum against gram + and –
  • Ampicillin – Listeria
  • Vancomycin – Cephalosporin-resistant streptococci

Take three

• blood culture
• lactate
• urine output

However your diagnosis is only confirmed after you have received the blood cultures back from the lab, so what should you do in the meantime?

Your differential for altered mental status and fever include:

• Bacterial meningitis
• Viral meningitis
• Viral encephalitis (usually HSV)
• Toxoplasmosis and cysticercosis (usually in IV drug users and endocarditis)
• Brain abscess
• Subarachnoid haemorrhage
• Ruptured aneurysm 

The things to check first are the things that are going to kill your patient within minutes, before you can get any imaging or lab results back:

• oxgen
• ischaemia

So check their sats, give oxygen as part of your sepsis six and order an ECG.

The next thing to worry about is blood glucose – a very common cause of altered mental status, so do a glucose test.

Next, you’re thinking about slightly longer term processes, such as intracranial haemorrhage, that will kill your patient, but you need to confirm before you manage them. So you can send your patient for a head CT, which should show you any evidence of haemorrhage.

If this comes back clean, then your suspicions of meningitis or encephalitis start to rise, so you do a lumbar puncture… but what do the results mean!?

Interpretting CSF results

The principles of CSF interpretation are fairly simple:

• White Cell Count
  • Usually below 5 and increased in infection
  • More increased in bacterial than in viral infection (>500 suggests bacterial)
• Cell differential
  • If you have a raised white count, the type can tell you bacterial vs viral
  • Bacterial tends to induce more polymorphonucleocytes
  • Viral will give a massive proliferation of lymphocytes
• Red blood cells
  • Normally shouldn’t be any, usually some in infection
  • The key here is a huge red cell count in the presence of minimal white cell elevation is strongly suggestive of herpes encephalitis
  • you also want to consider subarachnoid haemorrhage and ruptured aneurysm, however you’d hope these were picked up on the CT
• Protein
  • Generally elevated in infection
• Glucose
  • bacteria eat up lots of glucose, so a low CSF glucose suggests bacteria are present
  • Viral infections usually have a normal glucose level
• Opening pressure
  • Pressure increases in bacterial infection, and is usually normal in viral infection
• Gram’s stain
  • 80% of the time in bacterial meningitis you will be able to visualise organisms in the CSF
  • Beware the 20%!

Neonates – Group B streptococcus and Neisseria Meningitidis

Children and Adults – Streptococcus pneumoniae, Neisseria meningitidis, Listeria monocytogenes

And finally – prophylaxis

Anyone who comes in with bacterial meningitis could very well have passed it on to those around them. Close contacts should be given adequate prophylaxis in the form of:

• Rifampicin 600mg (10mg/kg) every 12 hours for 4 doses
• or
• Ciprofloxacin 500mg in a single dose (only for adults)