CNS Infections Flashcards
What makes the immune system of the CNS unique?
The brain has no lymphatic system / B cell defence predominates over T cell defence / The BBB tightly controls the entrance of immune cells into the brain
What is the purpose of the unique immune system of the CNS?
To limit oedema and secondary damage during inflammation of the CNS
Untreated infection within the CSF may cause what?
Brain herniation and death / spinal cord compression and necrosis which can lead to paralysis
What is the difference between meningitis and encephalitis?
Meningitis is infection of the meninges / encephalitis is infection of neuronal and glial substance of the brain (i.e. the parenchyma)
What is encephalopathy?
Irritation of brain parenchyma, not inflammation
What is the most serious form of meningitis?
Bacterial meningitis
Bacterial meningitis should be suspected in any patient presenting with features of what? Give examples.
Meningism (headache, neck stiffness, photophobia) and sepsis (fever, non-blanching purpuric rash)
What is a common presenting triad of bacterial meningitis?
Headache, fever and cognitive changes
What usually precedes an episode of bacterial meningitis?
A prodrome of a respiratory or ear infection
Bacterial meningitis occurs with peaks in who?
Infants and adolescents (freshers)
Where can the pathogenesis of bacterial meningitis come from?
Nasopharyngeal colonisation, direct extension of bacteria (e.g. sinusitis, mastoiditis, skull fractures) or from remote foci of infection (e.g. endocarditis or pneumonia)
Pyogenic meningitis is another name for bacterial meningitis - what does this refer to?
A thick layer of supperative exudate which covers the leptomeninges over the surface of the brain
Microscopically, pyogenic meningitis can be seen as what?
Neutrophils in the subarachnoid space
When should treatment for suspected bacterial meningitis be started?
Ideally within 1 hour - don’t wait for investigations!
What are the 4 main investigations to do for bacterial meningitis?
Bloods, throat swab, CT, LP
What bloods are done for bacterial meningitis?
FBCs, Us+Es, LFTs, WCC, CRP, culture, pneumococcal and meningococcal PCR
Name some patient groups who should undergo a CT to exclude a space occupying lesion before having a lumbar puncture?
Immunocompromised, history of CNS disease, new seizure, papilloedema, abnormal conscious level or focal neurological deficit
What is the purpose of the LP for bacterial meningitis?
To confirm the diagnosis and guide antibiotic therapy
After an LP, what tubes should you send off for interpretation?
2x (tubes 1 and 4) haematology for cell count and differential / tube 2 to microbiology for gram stain and culture / tube 3 to chemistry for glucose and protein
What would be the suspected opening pressure on LP in bacterial meningitis?
Slightly raised
Explain the main LP findings you would see in bacterial meningitis?
Raised WCC, neutrophils and protein, low glucose
What 4 organisms make up most of the cases of bacterial meningitis?
Haemophilus influenzae, strep pneumoniae, neisseria meningitides, listeria monocytogenes
Where is strep pneumoniae normally found in the body?
Nasopharynx
Which patients are more susceptible to infection with strep pneumoniae?
Hospitalised patients, skull fractures, diabetics/alcoholics, young children