M8 Central Nervous System Infections Flashcards
What body barriers are crossed in the conditions meningitis and encephalitis respectively?
Meningitis
blood-cerebrospinal fluid (CSF) barrier crossed
Encephalitis
blood-brain barrier crossed
What are the three meninges layers and their location?
Meninges layers are
- Dura mater (outer)
- Arachnoid
- Pia mater (inner)
Meninges are in between brain and skull bone, to protect brain and spinal cord.
What are the five different types of CNS infections?
- Blood borne - hematogenous spread: most common
- Nearby infections - Direct spread from infected site close to CNS
- Anatomic defects - Resulting from trauma, surgery or abnormalities
- Intraneural - Along nerves leading to the brain (least common)
- Abscesses - Brain abscesses can lead to meningitis (meningoencephalitis)
Primarily enter through bloodstream subarachnoid space: they cross the Blood-brain barrier
What is the pathogenesis of organisms getting into the CNS?
- Through the loss of capillary integrity of the blood-brain barrier
- Through the transport of circulating phagocytic cells
- By crossing the endothelial cell lining within endothelial cell vacuoles
What virulence factors or organisms primarily affect the CNS?
Primary virulence factors
1. encapsulated strains
2. pili
3. IgA proteases
4. endotoxins
What are the two major categories of meningitis?
- Septic (Purulent)
Significant, acute inflammatory exudative CSF with many polymorphonuclear (PMN) leukocytes (or neutrophils) - Aseptic
Usually viral and characterized by an increase in lymphocytes
What are the symptoms of acute meningitis?
Symptoms
- Fever
- Stiff neck
- change in mental status
- Rapid onset
Adult Symptoms
include “stiff neck”, extreme malaise, nausea, rapid onset headache
What are the symptoms of chronic meningitis?
Symptoms
are the same as acute meningitis.
- Slow onset
Often occurs in patients who are immunocompromised.
What is Brudzinki’s sign and Kernig’s sign for adult meningeal irritation respectively ?
- Brudzinki’s sign: Dr. raises head towards chest while patient is lying down (supine) and patient involuntarily flexion of their hips and knees.
- Kernig’s sign: While patient is lying down (supine), Dr. raises one leg up and if the patient indicates their back hurts it is a positive kernig sign.
What are some signs of meningitis in toddlers/infants?
Toddlers/Infants:
1. irritability
2. change in feeding
3. inability to focus
4. fontanel (indicating inflammation of brain)
5. petechial rash
6. Stiff body, jerky movements, or floppy, weak body.
What is a common cause of encephalitis? What is a potential bacterial cause of a brain abscess.
Viruses
CSF’s are usually negative, with low cell counts, immunocompromised patients. It can move to a meningo-encephalitis. Brain abscess: bacteria rarely (Citrobacter can cause abscesses).
What is a potential bacterial cause of a brain abscess?
Brain abscess: bacteria rarely but - Citrobacter can cause abscesses.
How are CSF specimens collected?
- Site preparation is similar to venipuncture; chlorohexidine gluconate alternate to iodine
- 3 tubes normally sent;
- labeled as to time, date, site of draw (lumbar puncture, ventricular shunt)
What is required for fungal and acid fast bacilli investigation compared to other CSF samples?
Increased volume required for fungal and AFB (acid fast bacilli) investigation
What tube is used for microbiology from a CSF specimen collection?
2 for microbiology
What would you expect to see in a purulent infection of CSF?
- Leukocytes - high, 5-20,000/mm^3
- PMNs predominant cell type
- Proteins elevated.
- Glucose - low, but may be normal in early course of disease.
Study slide 13 table for normal CSF, viral infected CSF, and TB & Fungal infected CSF.
Should you refrigerate CSF?
Don’t refrigerate CSF samples, as many
organisms are labile if refrigerated.
Also they are processed ASAP.
What is looked at in the macroscopic appearance of CSF?
Evaluate for volume and macroscopic appearance:
1. clear
2. cloudy
3. bloody
4. xanthochromic
What do you do with CSF if there is sufficient quantity?
if sufficient quantity, centrifuge
After centrifuge, what can be done with the supernatant?
Supernatant may be kept for serology and chemistry
How is CSF processed in the micro lab?
CSF sediment is examined for cells and organisms.
- Gram stain
- AFB
- Culturing from sediment or cytospin.
- Acridine orange
- Wet preparation
- India ink (Cryptococcus neoformans)
What type of test is used for CSF to check for C. neoformans?
Latex agglutination test used for C. neoformans
What do you do for CSF if you can not cytospin?
If not, one drop (do not spread), let dry, fix with methanol, read whole slide.
How does India ink help to detect C. neoformans?
India Ink give brown/blackish background.
India Ink cannot penetrate the capsules of C. neoformans.
What typical media is used to culture CSF?
- BA, CA, thioglycolate (or Ped Blood bottle)
- Fungal culture add Sabouraud Dextrose
What is done for CSF suspected of being infected with mycobacteria (TB)?
Mycobacteria (TB):
1. Do Kinjoun smear,
2. plant directly to LJ media and 3. Bact-alert TB bottle or other automated method
How far do you work up CSF cultures?
Full Identification required (all isolates)
Involve serotyping, example:
Neisseria meningitidis: several serotypes
How are CSF specimens reported?
Reporting - “panic value”: the most critical specimen
Information as obtained must be communicated.
What organisms are neonates susceptible to infections in their CSF?
Neonates: Gr B Strep, E. coli, Listeria
What organisms are 1 month to 5 y/o children susceptible to infections in their CSF?
1 month-5 y/o: H. influenza not type b, Strep. pneumoniae, N. meningitidis
What age group does N.meningitidis, S.pneumo, Listeria, S.aureus tend to infect the CSF of?
Young adults to adults
E.coli can affect the CSF of what two age groups?
Elderly (& other GNB)
and neonates
What organisms are the CSF of immunocompromised patients most susceptible to?
Immunocompromised: Cryptococcus neoformans, Listeria, TB
What are the potential pathogens to the CSF post surgery?
Post surgery: E. coli, K. pneumo, Staph (including CNS)
What can be a cause of fungal meningitis in suppressed immunity patients with a chronic lung infection?
CSF-fungal meningitis: Cryptococcus neoformans
suppressed immunity implicated in chronic infection
lung –>CNS
How is C. neoformans identified?
Identification:
- Urea pos
- Germ tube neg
- Carbohydrate assimilation (API)
- Phenol oxidase pos (caffeic acid is broken down by phenol oxidase producing melanin (dark brown)
What is an immunoassay method for detecting C. neoformans?
C. neoformans ID
capsular antigen detection
CSF specimens that yield positive results for cryptococcal antigen should be tested with a second latex agglutination test for rheumatoid factor.
Rheumatoid factor can give a positive results so must be inactivated or if positive (as test kits test for it as well) called uninterpretable.
What is useful for monitoring a patient’s response to treatment for a CSF C. neoformans infection?
Serial dilution protocols due to prozone phenomenon.
Dilute CSF to see what dilution is positive. Then compare the required dilution through stages of treatment.
Describe the epidemiology of carriers of CSF-Neisseria meningitidis?
- Can colonize carriers for long time
- Higher carrier rates in confined populations
- Direct contact or droplets from carrier
- Cause acute and epidemic meningitis
- Prophylactic treatment of close contacts
- Can be dangerous (death)
