Neuro Infectious Diseases Flashcards
overview of CNS infections
*life-threatening problems with high associated mortality and potential long-term morbidity
*presentation may be acute, subacute, or chronic
*clinical findings dictated by anatomic site(s) of involvement, infecting pathogen, and host response
anatomic structures that may be involved in CNS infections
-meningitis (inflammation of meninges)
-encephalitis (inflammation of brain)
-brain abscess/cerebritis (focal pocket of infection in the brain)
-epidural/subdural empyema (pocket of purulence in a space; can be in brain or spinal cord)
routes of CNS infection
- blood-borne spread from remote site of infection or site of mucosal colonization
- direct spread from contiguous focus
- access via anatomic defects
- direct inoculation (trauma, transplantation of infected tissues)
- entry via intraneural pathway (ex. herpesviruses)
blood-borne spread - route of CNS infection
*most common route of entry for CNS infections
1. microbes enter blood from sites of remote infection (i.e. lungs) or mucosal colonization (i.e. nasopharynx) and invade CNS
2. organisms must avoid host defenses in blood, be able to attach to neuroendothelial cells, and penetrate the blood-brain barrier
examples of common organisms that cause CNS infection due to blood-borne spread
- S. pneumoniae*
- N. meningitidis
- H. influenzae
- enteroviruses (Coxsackie, polio, echovirus)
NOTE - encapsulated bacteria have better evasion strategies to avoid host defenses
direct (contiguous) spread - route of CNS infection
organisms penetrate CNS from contiguous focus of active infection (sinusitis, dental abscess, osteomyelitis of skill base)
examples of common organisms that cause CNS infection due to direct/contiguous spread
- S. pneumoniae
- H. influenzae
- alpha-streptococci
- anaerobes
anatomic defects as a route of CNS infection
*organisms take advantage of breaches in physical barriers to enter CNS
*defects may be traumatic, surgical, or congenital in origin
*examples include basilar skull fractures, neurosurgical wounds, and dermal sinus tracts
examples of common organisms that cause CNS infection due to anatomic defects
S. pneumonia
others include H. flu, alpha strep, and anaerobes
factors that make the CNS an immunologically compromised organ system
- no intrinsic lymph node-lymphatic system
- restricted mobilization of traditional host defense components (PMNs, immunoglobulins) due to the blood-brain barrier
- restricted entry of antimicrobial agents due to relative impermeability of cerebrovasculature
time course of bacterial CNS infection
acute (hours to a couple days)
time course of viral CNS infection
subacute (several days)
time course of other (fungal, etc) CNS infections
subacute to chronic
CSF response of bacterial CNS infection
purulent (neutrophilic) CSF response
CSF response of viral CNS infection
lymphocytic CSF response
important bacterial causative organisms of CNS infections
strep pneumo
n meningitidis
listeria monocytogenes
strep agalactiae (esp in neonates)
important viral causative organisms of CNS infections
enteroviruses
HSV and other herpesviruses
arboviruses (west nile, etc)
important other causative organisms of CNS infections
mycobacterium tuberculosis
treponema pallidum (syphilis)
cryptococcus neoformans
coccidioides immitis
toxoplasma gondii
important microbial factors in pathogenesis of CNS infections
-capsules that resist phagocytosis
-IgA protease that inactivates IgA immunoglobulin at mucosal surfaces
-resistance to natural killing activity of serum
-fimbria/pili that attach to endothelial cells
-tropism for neural tissues
common bacterial pathogens in neonates (< 1 month)
- group B strep
- E. coli
- listeria monocytogenes
common bacterial pathogens in children (1 month - 20 years)
1 = N. meningitidis
2 = S. pneumoniae
common bacterial pathogens causing meningitis in adults (> 20 years)
1 = S. pneumoniae
2 = N. meningitidis
3 = listeria monocytogenes (esp. age 50+ or immunocompromised patients)
exam tipoff for CNS infections: Summer/Fall
arboviruses & enteroviruses
exam tipoff for CNS infections: siblings with meningitis
1 = N. meningitidis
# 2 = H. influenzae
exam tipoff for CNS infections: swimming in freshwater lake/rapids
amoebaes (Naegleria fowleri)
exam tipoff for CNS infections: handling rodents
lymphocytic choriomeningitis virus (LCMV)
exam tipoff for CNS infections: exposure to pigeons
cryptococcus
exam tipoff for CNS infections: exposure to other people with TB or TB-endemic area
M. tuberculosis
exam tipoff for CNS infections: prior meningitis
S. pneumoniae
exam tipoff for CNS infections: head trauma
1 = S. pneumoniae
other: gram neg rods, staph aureus
“classic findings” of CNS infections
*fever, headache, meningismus, altered mental status [2 of 4 present in ~95% of patients]
other: exanthems (rash), contiguous foci of infection, focal neurological signs (esp palsies of CN 3, 4, and 6)
Kernig’s sign for nuchal rigidity
*Kernig = Knee (K & K)
1. flex the knee and hip in a 90 degree angle
2. slowly extend the knee
3. sign considered present if resistance or pain (in back, neck, or head) occurs
Brudzinki sign
- bring chin to chest
- sign considered present if this causes flexion of hips
what is the single most important diagnostic test in patients with suspected CNS infection
LUMBAR PUNCTURE for analysis of CSF
note - also obtain blood cultures for all pts
contraindications for lumbar puncture
-cellulitis overlying LP site
-increased ICP (stupor/coma, papilledema)
-trauma/mass involving lumbar vertebrae
-thrombocytopenia/bleeding diathesis
how do we evaluate the CSF from lumbar punctures
-color/clarity
-cell counts/WBC and differential
-chemistries (protein + glucose)
-stains and smears (gram)
-cultures (bacterial)
-multiplex PCRs/antigen screens (if pt has WBCs present)
CSF profile for BACTERIAL infections of CNS
neutrophilic + LOW glucose (purulent)
CSF profile for VIRAL infections of CNS
lymphocytic + NORMAL glucose
CSF profile for OTHER (TB or fungal) infections of CNS
lymphocytic + LOW glucose
empiric treatment for bacterial meningitis
vancomycin + 3rd generation cephalosporin +/- ampicillin
notes:
vanco is for drug resistant strep
cephalosporin is for S. pneumo, N. meningitidis, H. flu
ampicillin covers for L. monocytogenes
what is the most common type of meningitis
aseptic (viral) meningitis
treatment for viral/aseptic meningitis
usually supportive and symptomatic only
viral encephalitis - common etiologies
HSV encephalitis, enteroviruses, and arboviruses
principles of management for CNS infections
*prompt decision-making is essential (once dx is considered, start antibiotics ASAP)
*obtain CSF (unless contraindicated)
*use cidal antimicrobial therapies with good CNS penetration
*add steroids with suspected bacterial meningitis
*isolate pts with N. meningitidis
