CNS infections Flashcards
What are the unique aspects of the CNS relevant to infections?
- no regeneration capacity
- fixed space (absence of drainage mechanism)
- blood brain barrier
- lack of WBCs (microglia replace them)
- very specific function in each region
Function of BBB in CNS infections
Normally, Protects the CNS from acute physiologic status change and toxin exposure.
** Inflammation (due to cytokines) increases the permeability of the BBB to certain antibiotics!!
3 routes of infection into the CNS
- Hematogenous (vast majority of community acquired bacterial CNS infections)
- Contiguous (from neighboring anatomical site (eg, trauma to skull, severe sinus infection)
- Ascending (from peripheral nervous system, eg HSV)
What 2 kinds of organisms have the ability to survive in bloodstream and stick to the meninges/brain?
- encapsulated organisms
- intracellular organisms (listeria and viruses)
Which encapsulated organisms are capable of infecting the CNS?
- Neisseria meningitidis
- streptococcus pneumoniae
- H. influenzae
- Cryptococcus neoformans
What mechanism is the cause of neck stiffness and positive Kernig/Brudzinski sign in meningitis?
Inflammation!
Why does headache/back pain occur in CNS infection?
increased intracranial pressure.
What is the jolt accentuation sign for meningitis?
It is when you shake someone’s head, and it is positive if their headache gets worse.
Very sensitive, but not very specific.
Key parts of the physical exam for CNS infection
- meningeal irritation (Kernig/brudzinski/neck stiff)
- intracranial hypertension (fundoscopic exam)
- focal neurologic sign (neuro exam)
**REPEAT these tests over a few hours in pt’s you are concerned about.
Appearance of papilledema
fuzzy optic disc, as opposed to the normal, clearly demarcated disc.
What is the single most important diagnostic test for meningitis?
lumbar puncture. Do it whenever meningitis or encephalitis is suspected clinically.
contraindications for lumbar puncture -4
- intracranial mass lesion
- intracranial hypertension
- severe thrombocytopenia (bleeding)
- agitated patient
When should a CT scan (with contrast) be used before lumbar puncture?
A CT scan can determine that a lumbar puncture is safe.
- any focal neurologic sign
- any known intracranial pathology
- immunocompromised host
- papilledema
**These are all signs of possible intracranial mass (first 3) or elevated intracranial pressure (papilledema)
You suspect meningitis. What is the next step?
First, do a rapid physical exam get blood culture.
-Then, do a lumbar puncture and start empiric antibiotics.
When is a brain / meningeal biopsy used?
- as a last resort
- most commonly used to differentiate chronic infection vs. tumor
4 most common symptoms of bacterial meningitis
- headache
- fever
- nuchal rigidity
- altered mental status
T/F - Meningitis is clinically indistinguishable from other forms of sepsis in a neonate.
True. Suspect meningitis in any febrile illness in a newborn!
Normal CSF labs vs. Bacterial Meningitis vs. viral meningitis
Normal - 0-5 WBCs, glucose 40-80, predominantly mononuclear cells.
Bacterial - 1000-5000 WBCs, glucose 40, predominantly mononuclear cells
two common meningitis pathogens for birth - 2 years old
Group B strep
E coli
Two common meningitis pathogens for 2 years old to 50 years old
Strep pneumo
Neisseria meningitidis
Empiric antibiotic therapy for meningitis in age group -
Ampicillin (for listeria)
+
third gen cephalosporin
(all intravenous!)
Empiric antibiotic therapy for meningitis in age group - 1-23 months
Vancomycin
+
third gen cephalosporin
(all intravenous!)
Empiric antibiotic therapy for meningitis in age group - 2-50 years
Vancomycin
+
third gen cephalosporin
(all intravenous!)
Empiric antibiotic therapy for meningitis in age group - >50 years.
Vancomycin \+ third gen cephalosporin \+ ampicillin (for listeria)
(all intravenous!)
Use of steroids in meningitis
Indicated for practically all suspected bacterial meningitis. HOWEVER - you must start it at the same time as antibiotics.
How do steroids help in meningitis?
they suppress severe inflammatory reaction in the CSF space, reducing damage from the infection.
Most common cause of encephalitis
Viruses.
Treatable causes of encephalitis
- HSV
- bacterial
Most causes are not treatable
When should you suspect encephalitis?
- any unexplained brain parenchymal lesion
- especially when it is not consistent with neurovascular anatomy.
Presentation of HSV encephalitis
-Fever and personality change
Treatment for HSV encephalitis
high dose acyclovir
You suspect encephalitis. What is the next step?
- Start acyclovir immediately, without waiting for test results!!
- Any pt with encephalitis needs to be considered to have HSV until proven otherwise.
Diagnostic test for HSV encephalitis
PCR on CSF fluid - very sensitive/specific.
Important consideration for empiric therapy in brain abscess
look for the primary site of infection - this can help you start appropriate therapy.
T/F if you suspect brain abscess, you should do a CT without contrast
False. with contrast
You suspect a brain abscess. What should you do and why?
Call Neurosurgery!
they can help with:
-possible drainage
-aspiration to establish diagnosis.
Who does listeria monocytogenes infect (for meningitis)
the very young (newborns) and the old
how to treat listeria monocytogenes?
ampicillin
