30 - CNS Infections Flashcards
Types of CNS infections
Meningitis (most important) Encephalitis (second-most important) Myelitis (spinal cord) Neuritis (nerves) Brain abscesses Subdural empyema Epidural abscess
Proportion of meningitis cases in less-developed countries
~96%
Case fatality of meningitis in less-developed countries
~50%
Age group in which meningitis is most common
Under one eyar
Age group in which meningitis case fatality ratio is highest
Over 65 years old
Aseptic meningitis
Inflammation of the meninges not caused by bacteria (mostly viral).
Can be non-infectious: malignancy, drugs (NSAIDs), inflammatory conditions.
Main viral causes of meningitis
Enteroviruses (coxsackie, echo)
Herpes viruses are less common (HSV, CMV, VZV, HHV6, EBV)
Are bacteria or viruses more likely to cause meningitis?
Viruses
Treatment of viral meningitis
Self-limiting, no long-term consequences. Wait for it to subside.
Dangerous meningitises
Those caused by bacteria.
Three most common bacterial causes of meningitis
H influenzae, N meningitidis, S pneumoniae (all capsulated, can evade immune system)
N meningitidis morphology
G- diplococcus
Most common N meningitidis causing meningitis in the world
Type A.
Most common N meningitidis causing meningitis in developed countries
B and C
Bacteria causing meningitis encountered by neonates (meningitis in first 3 months of life)
E coli
Group B streptococcus
Listeria monocytogenes
Broad stages of bacterial invasion of meninges and resulting meningitis
1 - 10
- Colonisation of nasopharngeal mucosa
- Invasion of bloodstream
- Survival and multiplication
4 Crossing of BBB - Invasion of meninges
- Increased permeability of BBB
7/8. Pleocytosis and increased ICP - Release of proinflammatory compounds
- Neuronal injury
Pleocytosis
Abnormal numbers of lymphocytes in CSF
Symptoms of meningitis in children 1 2 3 4 5 6 7
Headache Nausea Stiff neck Photophobia Fever Seizures Altered mental state
Meningitis that can also present with rash
Meningococcaemia.
Gives a purpuric (non-blanching) rash
Diagnosis of bacterial meningitis
Look for bacteria in CSF
Normal CSF pressure
Under 150mm H2O
White cell count of normal CF
5x10^6/L
Protein in normal CSF
Under 0.4g/L
Glucose in normal CSF
Over 60% of that in blood
Good animal model for meningitis
Ferrets
Appearance of CSF in viral meningitis
Normal pressure and appearance. Increased white cel count Negative Gram stain Slightly increased protein Normal glucose
Appearance of CSF in bacterial meningitis
Raised ICP Cloudy appearance Very elevated white cell count Positive Gram stain Raised protein Decreased glucose
Appearance of CSF in TB meningitis
Raised ICP Cloudy CSF Elevated white cell count ZN positive stain Very increased protein Very decreased glucose
White cell count at which CSF becomes cloudy
Extremely elevated
Why can’t CSF samples be delayed?
Neutrophils and other white cells die off
Glucose decreases significantly with time
Gram stain in those with bacterial meningitis
Normal 40% of the time (bacteria just aren’t detected)
Can CSF values alone be used to diagnose bacterial meningitis?
No
Effect of antibiotic treatment on CSF
Normalise values except for white cell count, which remains elevated
Four things to consider when treating meningitis patients (in order of when to perform)
Resuscitation / Life support
Fluids (SIADH->moderate restriction)
Antibiotics
Steroids
Most common deficit on surviving bacterial meningitis
Hearing loss
What is not affected in meningitis?
Brain is not inflamed
Symptom of encephalitis that is almost always present
Altered mental state
Most common, and important cause, of encephalitis
HSV
How is HSV encephalitis treated?
Acyclovir
Meningoccus that is vaccinated against
Group C.
New vaccine for B (not given routinely in Australia)
