CNS Infections Flashcards
What are the ways in which one can get a CNS infection?
1) Haematogenous spread
2) Direct implantation
3) Local extension
3) PNS to CNS
How can you classify meningitis?
Acute
- Often bacterial
Chronic
- Weeks/months history
- Often TB or Cryptococcus
Aseptic
- Usually viral (coxsackie B, herpes)
- Most common infection of the CNS
What are the main bacterial causes of meningitis? Name some other types and their risk factors
- Neisseria meningitidis
- Streptococcus pneumoniae
- Haemophilus influenzae
Other
- Listeria: young/old
- Group B streptococcus: neonates
What are the clinical features of meningitis?
- Headache
- Photophobia
- Neck stiffness
- Vomiting
- Fever
- Focal neural signs
- Non-blanching rash (not always present)
What are the diagnostic investigations sent for in a suspected case of meningitis?
- Imaging (CT for speed)
- Blood cultures
- CSF
- Throat swab
- Potentially a PCR if necessary
What is the management of meningitis?
Before culture results:
- Ceftriaxone
- Corticosteroids (with advice)
- Add amoxicillin if at risk of listeria
- Add acyclovir if encephalopathic
Once cultures have arrived, narrow the treatment
What are the routes of transmission for encephalitis?
- Person to person (most common)
- Through a vector (e.g. mosquito)
What are causes of encephalitis?
Viral:
- Herpes
Bacterial:
- Listeria
Amoebic:
- Naegleria
Parasites:
- Toxoplasmosis
Describe some focal CNS infections. What are the risk factors associated?
Brain:
- Abscess
Spine:
- Pyogenic infections
Risk factors:
- Increasing age
- IVDU
- Diabetes
What is investigated in a CSF sample?
- Colour
- Cell count
- Chemistry (proteins and glucose)
- Gram staining/ZN staining
- Antigens
- Cultures
- PCR
Describe the colour, cell count (10^6/L), gram stain result, protein level and glucose level in a normal CSF sample
Colour: clear
Cell count: 0-5 leukocytes
Gram stain: negative
Protein: 0.15-4
Glucose: 2.2 - 3.3
Describe the colour, cell count (10^6/L), gram stain result, protein level and glucose level in a purulent meningitis CSF sample
Colour: turbid
Cell count: 100-200 neutrophils
Gram stain: positive (depending on pathogen)
Protein: higher than normal
Glucose: lower than normal
Describe the colour, cell count (10^6/L), gram stain result, protein level and glucose level in an aseptic meningitis CSF sample
Colour: clear
Cell count: 15-100 lymphocytes
Gram stain: negative
Protein: higher than normal
Glucose: normal
Describe the colour, cell count (10^6/L), gram stain result, protein level and glucose level in a tuberculosis meningitis CSF sample
Colour: clear/turbid
Cell count: 30-50 lymphocytes
Gram stain: negative (ZN stain positive)
Protein: much higher than normal
Glucose: lower than normal
