Intro to CNS Infection Flashcards
how does the blood brain barrier achieve its function?
interendothelial tight junctions, enzymatic barrier, efflux pumps, low levels of endo- and transcytosis
what cells are involved in the BBB?
capillary endothelial cells surrounded by pericytes, basal lamina, and astrocytes
what does it mean that the CNS is “immune privileged”?
there is restricted immunological defense: no lymphatics in brain, limited complement in the CSF, low MHC expression (restrict potential inflammatory reactions)
what CNS cells do express MHC?
microglia and perivascular macrophages
what is the role of astrocytes in the CNS?
express TLR4, produce TGFb – inflammatory activity and suppression
what is the role of microglia in the CNS?
highly phagocytic macrophages of CNS tissue, poor APCs, express TLR4, activated lead to inflammatory mediators (no DCs in brain, but microglia can morph to look like them)
what is the role of mast cells in the CNS?
produce TNF in the meninges, facilitate T cell entry during inflammation by increasing permeability of endothelial cells
name 3 potential health side effects of mast cell activity in the CNS
inflammation, autism, seizures
when can T and B cells enter the CNS?
only activated T cells stimulated in peripheral lymph nodes & activated B cells in response to inflammation-induced permeability of BBB
how do immune arcs in the CNS compare to the periphery?
there is a severely dampened afferent cellular arm, same afferent soluble, slightly decreased efferent cellular
what is encephalitis?
acute inflammation of brain parenchyma (could also have a brain abscess)
what is meningitis?
acute or chronic inflammation of the meninges
top microbial causes of acute meningitis
encapsulated bacteria (strep pneumo, n. meningitidis); arboviruses; enteroviruses; HSV2
major microbial causes of chronic meningitis
myco. Tuberculosis, cryptococcus neoformans (pathogenic encapsulated yeast), other fungi
microbial causes of acute brain abscess
staph, mixed flora, GAS
microbial causes of chronic brain abscess
myco TB, cryptococcus neoformans, taenia solium (cysticercosis), toxoplasma gondii
what are the three major entry routes for microbes in the CNS
blood via choroid plexus (more permeable, achilles heel), retrograde passage on neurons (or through olfactory nerve), direct inoculation from trauma or defects
name 3 ways that microbes can get into the blood circulation
colonization and penetration of mucosal epithelium, bite of an infected animal, transplacental
name a bacteria and a class of viruses that can directly infect endothelial cells in the brain
Rickettsia (RMSF) & arboviruses
name 4 important epidemiological factors that influence source of CNS infection
age, immunocompetence, geographic location, time of year
what microbes should be on the differential for bacterial meningitis in neonates?
Group B strep, E. coli, Listeria
what microbes should be on the differential for bacterial meningitis in healthy adults?
strep pneumo, neisseria meningitidis
what microbes should be on the differential for bacterial meningitis in an immunosuppressed patient?
listeria or gram negative rods
name three major components of CNS damage
- death of CNS cells from infecting microbe, 2. tissue destruction from host immune response, 3. cerebral edema from inflammation
major signs of frontal lobe abscess
sinusitis, HA, memory defects, attention loss, decreased intellect
major signs of temporal lobe encephalitis
personality changes, visual field defects, hemiparesis, focal seizures
major signs of basilar meningitis
suboccipital HA, neck stiffness, double vision, cranial nerve palsies
physical exam findings of CNS infections
neck and back rigidity, HA, vomiting, photophobia, Kernig’s sign, Brudzinski’s sign, mental status changes, decreased blood pressure
how to diagnose a CNS infection
- start on antibiotics just in case, 2. obtain blood cultures from 2 locations, 3. get CT right away, 4. get LP if no abscess or altered consciousness
describe the CSF findings in a person without any CNS infection
minimal WBCs, mononuclear predominance, CSF:blood glucose >0.5, protein 20-50
describe the CSF findings in a person with viral meningitis
10-1000 WBCs (varied), mononuclear predominance, normal glucose, protein 50-100 (high)
describe the CSF findings in a person with bacterial meningitis
1000-5000 WBCs (very high), neutrophil/PMN predominance, CSF:blood glucose <0.5 (low), protein 100+ (very high)
describe the CSF findings in a person with TB meningitis
100-500 WBC (high), lymphocyte predominance, low glucose, very high protein
describe the CSF findings in a person with cryptococcal meningitis
100-500 WBC (high), lymphocyte predominance, low glucose, protein 50-100 (high, but not as high as TB)
