Intro to CNS Infections

Question 1

What are the three big symptoms of CNS infections?

Answer 1

fever, headache, altered mental state

Question 2

What are the three main infectious causes of fever, headache and altered mental state?

Answer 2

meningitis

encephalitis

abscess

Question 3

What is encephalopathy?

Answer 3

Diffuse cerebral dysfunction WITHOUT inflammation – probably due to toxin or metabolic dysfunction

Question 4

Why are infections of the CNS uncommon?

Answer 4

• 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

Question 5

In the CNS, is the immune response more innate or adaptive?

Answer 5

innate

Question 6

What are 4 characteristics of microbial invasion to the brain?

Answer 6

1. hematogenous dissemination
2. contiguous spread from sinusitis, otitis media, or mastoiditis
3. trauma or congenital lesions make it easier
4. retrograde axonal transport (especially the viruses)

Question 7

How are CNS infections categorized?

Answer 7

where in the brian they occur

Question 8

What are the 4 main types of CNS infections and where do they occur?

Answer 8

meningitis = subarachnoid space

encephalitis = diffuse parenchyma

abscess = focal parenchyma

myelitis = spinal cord

Question 9

What are the typical steps in diagnosis of a CNS infection?

Answer 9

1. History and physical
2. blood culture and EMPIRIC TREATMENT
3. Neuroimaging
4. Lumbar puncture/biopsy
5. Identificaiton of organism
6. antibiotic susceptibitility testing
7. switch to definitive treatment/supportive therapy

Question 10

If neuroimaging doesn’t get you much, why is it still good to obtain if you’re concerned about CNS infection?

Answer 10

It tells you if there’s too much cerebral edema to safely do a lumbar puncture

Question 11

What is the most common cuase of viral meningitis/encephalitis and when in the year does it occur most often?

Answer 11

enterovirus - usually in late summer to fall

Question 12

What are the perinatal CNS infections to be concerned about? Remember they can have mild maternal morbidity, but serious fetal consequences.

Answer 12

group B strep

E. coli

Listeria

TORCH: Toxoplasmosis, Other (symphilis, varicella zoster, parvovirus), Rubella, Cytomegalovirus and Herpes Infections (HSV-2)

Question 13

If you are worried about bacterial meningitis, how should you start?

Answer 13

1. take a blood culture first
2. treat with empiric antibiotic - BACTERICIDAL at 10-fold greater than minimum inhibitory concentration

Question 14

WHat characteristics do you want in a drug for CNS infections?

Answer 14

bactericidal, small, lipophilic, low affinity for plasma binding proteins, not a ligand for efflux pumps at the BBB

Question 15

What groups of patients have increased penetration of drugs thorugh the BBB?

Answer 15

newborns and individuals with CNS inflammation

Question 16

What are the three main classes ot antibiotics we should be worried about in terms of CNS toxicities?

Answer 16

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

Question 17

In terms of beta lactams, what patient factor would place them at higher risk for seizures?

Answer 17

decreased renal function - less excretion, buildup of drug, more likely to seize

Question 18

When should you obtain neuroimaging?

Answer 18

trauma

immunocompromised

focal neurologic findings

decreased conciousness

Question 19

If focal mass lesion is identified on neuroimaging, why shouldn’t you do an LP?

Answer 19

There will be high intracranial pressure, so risk of brain herniation is too much

Question 20

How can you tell with a WBC whether a meningitis is likely bacterial vs viral?

Answer 20

bacterial = more PMNs

viral = more lymphocytes

Question 21

Which is more common in meningitis - viral or bacterial? Which is more serious?

Answer 21

viral more common

bacterial more serious

Question 22

What additional symptoms will likely occur in encephalitis that don’t occur in meningitis?

Answer 22

motor and sensory deficits with potential progression to seizures, speech disturbances, lethargy and coma

Question 23

What percentage of encephalitis cases are of unknown etiology?

Answer 23

33-66%

Question 24

What do you empirically use to treat encephalitis?

Answer 24

acyclovir - until HSV ruled out

Question 25

What are the main viral causes of encephalitis/ Nonviral?

Answer 25

viral - enterovirus, arbovirus, HSV, Rabies

Nonrival - ricckettsia, mycoplasma, acute disseminated encephalomyelitis

Question 26

What will predispose someone to brain abscess formation?

Answer 26

pre-existing ischemia: necrosis begins as cerebritis and then becomes encapsulated

Question 27

Brain abscesses are often associated with mixtures of bacteria, including….

Answer 27

streptococci (most common)

pseudomonas

haemophilus

staphylococcus

bacteroides

Question 28

What determines localization of a brain abscess usually?

Answer 28

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

Question 29

How do you diagnose a brain abscess?

Answer 29

CT or MRI plus needle aspiration

blood cultures will usually be positive

LP is not beneficial

Question 30

What is the typical treatment for a brain abscess?

Answer 30

ceftriazone and metronidazole

add vanco for staph

may need surgey for pseudomonas