Intro to CNS Infections Flashcards
What are the three big symptoms of CNS infections?
fever, headache, altered mental state
What are the three main infectious causes of fever, headache and altered mental state?
meningitis
encephalitis
abscess
What is encephalopathy?
Diffuse cerebral dysfunction WITHOUT inflammation – probably due to toxin or metabolic dysfunction
Why are infections of the CNS uncommon?
- the scalp and skull protect it from external entry
- three meninges surround the brain and spinal cord
- tight junctions of BBB prevent organisms from entering the CNS
In the CNS, is the immune response more innate or adaptive?
innate
What are 4 characteristics of microbial invasion to the brain?
- hematogenous dissemination
- contiguous spread from sinusitis, otitis media, or mastoiditis
- trauma or congenital lesions make it easier
- retrograde axonal transport (especially the viruses)
How are CNS infections categorized?
where in the brian they occur
What are the 4 main types of CNS infections and where do they occur?
meningitis = subarachnoid space
encephalitis = diffuse parenchyma
abscess = focal parenchyma
myelitis = spinal cord
What are the typical steps in diagnosis of a CNS infection?
- History and physical
- blood culture and EMPIRIC TREATMENT
- Neuroimaging
- Lumbar puncture/biopsy
- Identificaiton of organism
- antibiotic susceptibitility testing
- switch to definitive treatment/supportive therapy
If neuroimaging doesn’t get you much, why is it still good to obtain if you’re concerned about CNS infection?
It tells you if there’s too much cerebral edema to safely do a lumbar puncture
What is the most common cuase of viral meningitis/encephalitis and when in the year does it occur most often?
enterovirus - usually in late summer to fall
What are the perinatal CNS infections to be concerned about? Remember they can have mild maternal morbidity, but serious fetal consequences.
group B strep
E. coli
Listeria
TORCH: Toxoplasmosis, Other (symphilis, varicella zoster, parvovirus), Rubella, Cytomegalovirus and Herpes Infections (HSV-2)
If you are worried about bacterial meningitis, how should you start?
- take a blood culture first
- treat with empiric antibiotic - BACTERICIDAL at 10-fold greater than minimum inhibitory concentration
WHat characteristics do you want in a drug for CNS infections?
bactericidal, small, lipophilic, low affinity for plasma binding proteins, not a ligand for efflux pumps at the BBB
What groups of patients have increased penetration of drugs thorugh the BBB?
newborns and individuals with CNS inflammation
What are the three main classes ot antibiotics we should be worried about in terms of CNS toxicities?
Aminoglycosides - ototoxicity thorugh activation of the NMDA receptors
Beta-lactams - inhibit GABAa release so you lose inhibition and become more prone to seizures
Macrolides - ototoxicity thoruhg damage to the cochlea
In terms of beta lactams, what patient factor would place them at higher risk for seizures?
decreased renal function - less excretion, buildup of drug, more likely to seize
When should you obtain neuroimaging?
trauma
immunocompromised
focal neurologic findings
decreased conciousness
If focal mass lesion is identified on neuroimaging, why shouldn’t you do an LP?
There will be high intracranial pressure, so risk of brain herniation is too much
How can you tell with a WBC whether a meningitis is likely bacterial vs viral?
bacterial = more PMNs
viral = more lymphocytes
Which is more common in meningitis - viral or bacterial? Which is more serious?
viral more common
bacterial more serious
What additional symptoms will likely occur in encephalitis that don’t occur in meningitis?
motor and sensory deficits with potential progression to seizures, speech disturbances, lethargy and coma
What percentage of encephalitis cases are of unknown etiology?
33-66%
What do you empirically use to treat encephalitis?
acyclovir - until HSV ruled out
What are the main viral causes of encephalitis/ Nonviral?
viral - enterovirus, arbovirus, HSV, Rabies
Nonrival - ricckettsia, mycoplasma, acute disseminated encephalomyelitis
What will predispose someone to brain abscess formation?
pre-existing ischemia: necrosis begins as cerebritis and then becomes encapsulated
Brain abscesses are often associated with mixtures of bacteria, including….
streptococci (most common)
pseudomonas
haemophilus
staphylococcus
bacteroides
What determines localization of a brain abscess usually?
where the infeciton started
otitis media goes to the temporal lboes and cerebellum
dental and isnus to the frontal love
hematogenous to multiple sites usually around the middle cerebral artery
How do you diagnose a brain abscess?
CT or MRI plus needle aspiration
blood cultures will usually be positive
LP is not beneficial
What is the typical treatment for a brain abscess?
ceftriazone and metronidazole
add vanco for staph
may need surgey for pseudomonas
