CNS infections Flashcards
(41 cards)
Difference between meningitis and encephalitis (bacteria or virus)
Meningitis: Inflammation of the meninges and subarachnoid space caused by bacteria.
Aseptic meningitis: Non-bacterial causes
Encephalitis: Inflammation on the brain typically caused by a virus.
Define the meninges and the fluid filled spaced between them
Meninges: Pia, arachnoid and dura mater
Subarachnoid space is the space between the arachnoid and pia mater
What 3 mechanisms do the brain use to control its composition
BBB, CSF formation, Glial cell conditioning
List the components of the BBB
It is the physical barrier that prevents diffusion of disruptive substances from the blood into the brain extracellular fluid. Tight junctions join adjacent cells along the length of the brain capillaries.
What are the 3 communication barriers between the blade and the brain extracellular fluid
The presence of think basement membrane that coats endothelial cells, processes/endfeet of astrocytes continuously covers the capillary, parasites in the basement membrane modulate endothelial and astrocytic functions.
Explain how CSF is formed and the pathway of the CSF through circulation
CSF is formed by the choroid plexus. From the choroid plexus, CSF circulates through the ventricles, enters the subarachnoid space, and exits into the venous system. Choroid plexus tightly regulates CSF composition.
What are the 5 functions of astrocytes
Produce and deliver nutrients to neurons, regulate extracellular K+ levels, synthesize and recycle NT, promote survival of neurons by secreting trophic factors, form the BBB
What are the 2 functions of oligodendrocytes
Myelinate neuronal axons and regulate pH and iron metabolism
What are the 2 functions of microglia
Phagocytose bacteria and damaged cells, present antigen to T cell
How can infectious pathogens enter the CNS (4 methods)
- Carried in the blood (hematogenous spread)
- direct implantation through trauma or congenital malformations
- infected tooth or sinuses spreading to CNS
- transport along peripheral nervous system
Explain the mechanism by which pathogens cause damage to the CNS
Directly from pathogen, indirectly from microbial toxins, inflammatory mediators and immune-mediated mechanisms
Damaged endothelium can result in ischemic necrosis
Most common bacterial etiologies in < 1 month, 1-23 months, 2-50 years, >50 years, immunocompromised, any age with penetrating head trauma or infection of neurosurgery)
<1 month: S. agal, E. coli, Listeria
1-23 months: S, agal, E. coli, H. influenzawe, S. pneumo, N. meningitidis
2-50 years: S. pneumo, N. meningitidis
>50 YO: S. pneumo, N. menin, Listeria, E. coli
Immunocompromised: Listeria
Head trauma: S. aureus, P. aeruginosa
Explain the staining characteristics of S. agal, E. coli, Listeria, H. influenzae, S. pneuma and N. meningitidis
S. agal: Gram-pos Cocci in pairs (B-hemo)
E. coli: GNR (lactose positive)
Listeria: Gram-pos rods
H. influenzae: GNR
S. pneumo: gram pos diplococci (a-hemolytic)
N. meningitidis: Gram neg cocci
Clinical presentation of bacterial meningitis
Infants: Irritability, altered eating/sleeping patterns, crying, vomiting, seizures
95% of patients will have 2 of the following 4 symptoms: Fever, stiff neck, altered MS, HA
Other symptoms: Photophobia, N/V, seizures
What are the 2 specific signs of meningitis
Kernigs: Inability to straighten knee from bent position
Brudzinskis: Severe neck stiffness causing hips and knees to flex when head is fixed
What are the 4 goals of therapy for the treatment of meningitis?
Start prompt empiric therapy, improve signs and symptoms, eradicate infection, prevent development of neurological sequelae
What is the appropriate empiric therapy for most patients (non immunocompromised, and between the ages of 1 month and 50 years)
3rd gen ceph (Ceftriaxone or cefotaxmine) + Vanco with or without rifampin
What is the appropriate empiric therapy for those < 1 month, >50 years or immunocompromised
3rd gen ceph (Ceftriaxone or cefotamine) + Vanco + Ampicillin with or without rifampin
In which patient population should ceftriaxone be avoided and why
Avoid in hyperbilirubinemic neonates (< 1 month) and should not be given with IV calcium containing products in neonates because risk of calcium deposition in organs
How long should empiric therapy continue?
At least 2-3 days or until diagnosis of bacterial meningitis is ruled out
When should gentamicin be added to treatment regimens?
Infants < 1 month of age
What are the appropriate doses of cefotaxime, ceftriaxone, vancomycin and ampicillin
Ceftriaxone 2 grams Q 12 H
Cefotaxime 2 grams Q 4-6 H
Vanco 15mg/kg (target trough 15-20)
Ampicillin 2 grams Q 4 H
Which microbial pathogens commonly seen in are covered by ceftriaxone, cefotaxime, vanco, and ampicillin
Ceftriaxone: S. pneumo, H. influenzae, N. meningitidis
Cefotaxime: Same as ceftriaxone
Vanco: Extensive gram + coverage (S. pneumo, S. agal)
Ampicillin: Drug of choice for Listeria and susceptible strains of N. meningitidis and H. influenzae
For the third generation cephalosporins, which MIC values for S. pneumo correlate to resistant, susceptible and intermediate
MIC < 0.5 = Susceptible
MIC 1 = intermediate
MIC > 2 resistant
