Flashcards in CNS INfections...long Deck (28):
Kid comes in confused (global cortical dysfunction), drowsy (ascending arousal system of midbrain and thalamus is screwed up), and with stiff neck (meningeal inflammation). Also has rash consistent with inflammation of small blood vessels (small vessel vasculitis).
This is a classic presentation for
DISASTER>...can kill in hours
Treat empirically (before diagnosis)
Bacterial meningitis can be caused by pathogens that get into the meninges how?
- blood borne and arrive from another infected location like the lungs
- May enter from a nearby infected structures, say the ear, when veins clot as in the case of otits media or mastoiditis
- direct entry from outside
How do bacteria cross BBB
capsule and pili are the most important virulence factors here. They penetrate endothelial cells and cross BBB
Once inside the CSF, the environment is perfect for bacteria because there are few immune cells on patrol and plenty of glucose
within hours the immune cells arrive in CSF
inflammatory respponse mediated by
IL-1 and TNF-Alpha....this inflammatoion results in small vessel vasculitis and thrombophlebitis with decrease in cerebral blood flow.
- Ischemia then leads to infarction with greater swelling
- Results in small vessel vasculitis and thrombophlebitis with consequent decrease in cerebral blood flow
- BBB breaks down
- increase in ADH leads to low sodium concentration and blood becomes hypo-osmolar. This provides a source of free water that exacerbates edema
Whats important to realize about antibiotics in meningitis treatment?
They strongly stimulate the immune response by lysing the bacterial cell walls and releasing wall fragments that are highly antigenic. Cytokines, interleukins and inflammatory cascade occurs, vasculitis also occurs
How do you counter this poor side-effect of antibiotics?
children older than 2 mos and adults, most common causes of bacterial meningitis are
pneumococcus and meningococcus
Group B strep, Listeria (also in old ppl), E. Coli
When there is direct penetration of the CSF via surgery or trauma, what are some causative organisms
Staphylococcus and Gram negatives
The adrenal glands can be affected by meningitis. What hapens
They undergo hemorrhagic necrosis and you get an Addisonian crisis due to low corticosteroids...called waterhouse friedrichsen syndrome
Listeria risk factors
whatever depresses the immune system....pregnancy, organ transplant, autoimmune disease, etc...
inability to straighten the knee with the patient supine and the hips flexed at 90 degrees
passive flexion of neck causes flexion of both legs and thighs
What will labs show in bacterial meningitis?
- High White count on CBC and a marked increase in neutrophils
- Left shift
- Serum sodium may fall due to SIADH
- Prothrombin time and INR become elevated due to consumption of clotting factors in DIC
- Cultures are taken of blood and of every potential site from which the infection may have originated
- KNOW>..SERUM PROCALCITONIN will be hihg as will C REACTIVE PROTEIN
A PCR test for the bacterial 16sribosomal DNA can confirm that the pathogen is bacterial
Best test for west nile
CSF profile in bacterial meningitis?
tons of pols (normally no more than 5), Neutrophils predominate, Glucose is low (normal 50-100), Protein is increased.
Treatment of bacterial meningitis causes the CSF profile to shift toward lymphocytic predominance
Treatment of bacterial meningitis
- Steroids FIRST! Dexemethasone within 15 minutes of ABs. The steroids suppress TNF and IL-1
- Then give antibiotics to treat different bugs
- withdraw these antibiotics as you narrow down what the pathogen is
Subacute bacterial endocarditis
usually gram positive cocci--- widespread septic embolism
Four ways bacterial endo can affect the brain
1) Sepsis- can cause metabolic encephalopathy producing confusion, delirium, and coma
2) Can occlude a large cereral blod vessel and cause ischemic stroke
3) Can produce a focal brain are of ischemia and inflammation
4) Can embolize to a distal cerebral artery and cause focal inflammatory erosion of the vessel wall and produce a mycotic aneurysm
What organism is responsible for approximately 50% of bacterial endocarditis
When do you not want to do a lumbar puncture due to risk of herniation?
When there is mass effect
Other signs of bacterial endo
- splinter hemorrhages
- Osler's nodes
- Janeway lesions
- Roth's spots