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
CNS devices e.g. cochlear implants are related to an increased risk of which bacteria?
Strep pneumoniae
N. Meningitides is an intracellular organism - within which cells is it found in the CNS? Symptoms from this organism are actually caused by what?
Leukocytes / an endotoxin
Who does N. meningitides meningitis mostly occur in?
Children and adolescents
Who is H. influenzae most likely to occur in?
Children (especially < 4)
Who are more at risk of getting meningitis caused by listeria?
Neonates and those aged > 55, and immunocompromised (especially malignancy)
What are some non-conventional agents that may cause meningitis in the immunocompromised?
Listeria, mycobacterium TB, cryptococcus
Cryptococcus neoformans most commonly causes meningitis in who? What type of organism is it? How is it treated?
Those with HIV and CD4 < 100 / fungus / amphotecerin B/flucytosin and fluconazole
What are some features which may raise suspicion of a TB meningitis?
Subacute onset, non-specific ill health, poor yield from CSF, CN palsies
Name 3 bacteria which are most likely to cause meningitis in neonates?
E.coli, group B strep, listeria
What organism is most likely to cause meningitis in children?
Haemophilus influenzae
What organism is most likely to cause meningitis in those aged 10-21?
Neisseria meningitides
What organisms are most likely to cause meningitis in those aged 21-65?
Strep pneumoniae and neisseria meningitides
What organisms are most likely to cause meningitis in those aged 65+?
Strep pneumoniae and listeria
People who have undergone recent neurosurgery or head trauma are more at risk of meningitis caused by what organisms?
Staphylococcus, gram - bacilli
People who have undergone a recent fracture of the cribriform plate are more at risk of meningitis caused by what organisms?
Strep pneumoniae
People who have a CSF shunt are more at risk of meningitis caused by what organisms?
Staph epidermidis/aureus, proprionibacterium acnes
What is the initial treatment (before antibiotics) for people presenting with bacterial meningitis?
ABCDE and start sepsis 6 if necessary
What are the major things that are covered in immediate hospital management of bacterial meningitis?
Take bloods, give antibotics, take throat swabs, swab or aspirate any skin lesions for microscopy and culture
What is the first medical management for bacterial meningitis?
Ceftriaxone 2g IV bd with dexamethasone 10mg IV qds
What is the first medical management for bacterial meningitis if the patient is penicillin allergic?
Chloramphenicol 25mg/kg IV qds with dexamethasone 10mg IV qds
When should dexamethasone be started for bacterial meningitis? When should it be used until?
At the same time or just before the first dose of antibiotics. If pneumococcal meningitis is confirmed, continue it for 4 days. If not then stop it.
When would a patient being treated for bacterial meningitis require extra cover against listeria? What is this cover?
If they are aged 60+ or immunocompromised (including alcohol dependency and diabetes) / amoxicillin 2g IV 4 hourly
What is the penicillin allergic option to cover listeria?
Co-trimoxazole 120mg/kg IV in 4 divided doses
If there has been recent travel within the last 6 months, what additional antibiotic would you start a patient who is being treated for bacterial meningitis on?
Vancomycin 15-20mg/kg bd IV or rifampicin 600mg bd IV/PO
Who, being treated for bacterial meningitis, should not receive steroids?
Post-surgery, immunosuppressed, hypersensitivity to steroids, meningococcal or septic shock
Gram + diplococcus implies which organism?
Strep pneumoniae
Gram - cocci implies which organism?
Neisseria meningitides
Gram - bacillus implies which organism?
Haemophilus influenzae (also E.coli)
Gram + bacillus implies which organism?
Listeria monocytogenes
Describe the onset of viral meningitis when compared to bacterial?
Slightly more subacute onset, potentially presenting over days
What is the outcome of viral meningitis?
It is usually self-limiting and patients recover without any neurological complications
Describe the presentation of viral meningitis?
Similar to bacterial but not as severe - often headache, fever and lack of significant neurological deficit with a mildly raised WCC
When is it more common to get viral meningitis?
Summer/late autumn
What is aseptic meningitis?
Essentially a term for any suspected meningitis which is not bacterial (could be viral, but not exclusively)
What are the main 3 investigations to do for viral meningitis?
CSF PCR, throat swab and viral stool culture
Why is a viral stool culture done in the investigation for viral meningitis?
Because often the causative virus is enteric to the gut
What is the most common organism to cause viral meningitis?
Enteroviruses e.g. coxsackie or echovirus
What is an important thing to ask about in suspected viral meningitis and why?
Travel history - lots of strange viruses which can cause this if the person has travelled
What is the treatment for viral meningitis?
Supportive
What are some viral agents which may cause viral meningitis in the immunocompromised?
EBV, CMV, toxoplasma gondii
Encephalitis is the inflammation of the brain parenchyma. What can it be caused by?
Any infectious agents or an autoimmune process
Encephalitis can co-exist alongside what other infections?
Meningitis (encephalomeningitis) or inflammation of the spinal cord (encephalomyelitis)
What is a sign that is a) more specific to meningitis than encephalitis? b) more specific to encephalitis than meningitis? c) if these are both seen together, what could be a cause?
a) neck stiffness b) confusion c) meningoencephalitis
What is the onset of encephalitis?
Usually has an insidious onset, though can sometimes be sudden
What are some potential presenting features of encephalitis?
Headache, fever, seizures, focal neurological deficits, deteriorated mental status
What is the most serious organism to cause encephalitis?
Herpes simplex
Herpes simplex encephalitis typically presents with what? This is due to inflammation where in the brain?
Seizures and memory/behavioural disturbance / temporal lobe
What investigations should be done for encephalitis?
Lumbar puncture, EEG, MRI
What will a lumbar puncture of encephalitis show?
Raised lymphocytes and protein, normal glucose
If there are delays in investigations for encephalitis, can treatment be started anyway?
Yes
What treatment is used for encephalitis? What is the dose of this for someone > 12 years old?
Acyclovir - 10mg/kg
What are the main complications of CNS infection?
Purulence, invasion, cerebral oedema, hydrocephalus
After/during a CNS infection, clusters of pus can form at the base of the brain. These can form exudate around nerves - which are most commonly affected?
CNs III and VI
What structure prevents meningitis from becoming an abscess? What can abscesses cause?
The pia mater / secondary vetriculitis and hence meningitis
What are the public health rules with regards to bacterial meningitis?
All cases should be reported to public health so that contact tracing can be performed for prophylaxis and vaccination
What should be done regarding recording close contacts of people with bacterial meningitis?
Their records should be labelled to alert doctors of their increased risk for 6 months
What is the main prophylactic regimen for adults aged 12+ who have been in close contact to those with bacterial meningitis?
Rifampicin PO 600mg 4 doses 12 hourly
What is the a second prophylactic regimen for people who have been in close contact to those with bacterial meningitis which is not licensed but has been used in epidemics?
Ciprofloxacin PO 500mg as a single dose
Vaccines exist for which causes of bacterial meningitis?
Haemophilus influenzae, strep pneumoniae and neisseria meningitides
What is the main meningococcal vaccination and who is it offered to?
MenACWY - offered to adolescents
What are polymorphs? These are suggestive of what diagnosis?
Neutrophils - bacterial meningitis
Pink coloured CSF suggests it is what? What diagnosis does this suggest?
Turbid - bacterial meningitis
High doses of steroids given short term can cause what?
Steroid psychosis / raised blood sugar
Milleri strep is suggestive of what?
Brain abscess
What warnings should you give to patients taking rifampicin?
Decreases efficiency of the contraceptive pill, turns body fluids red
