MI: CNS Infections and Meningitis Flashcards
What are the routes of entry into the CNS?
- Haematogenous
- Direct implantation
- Local extension
- PNS into CNS (rabies)
What is the most common route of entry for pathogens?
Haematogenous
What is aseptic meningitis?
Meningitis that is caused by viruses and is not purulent
What are the causes of neurological damage in meningitis
- Direct bacterial toxicity
- Indirect inflammatory response, cytokine release and oedema
- Shock, seizures and cerebral hypoperfusion
What are the three types of meningitis?
- Acute (hours to days) - bacterial
- Chronic (days to weeks) - TB and weird
- Aseptic (caused by viruses so there is no pus)
Name three organisms that cause acute meningitis.
- Neisseria meningitidis
- Streptococcus pneumoniae
- Haemophilus influenzae
How many serotypes of N. meningitidis are there?
N. meningitidis can be classified into 12 serogroups based on its capsular polysaccharide; serogroups A, B, C, W, X, and Y are the primary causes of meningococcal disease worldwide
List some other, rarer bacterial causes of acute meningitis.
- Listeria monocytogenes
- Group B Streptococcus
- Escherichia coli
How does N. meningitidis enter the body?
Through the nasopharyngeal mucosa in susceptible individuals
NOTE: only 1% of carriers of N. meningitidis have pathogenic strains
How long does N. meningitidis take to cause infection?
< 10 days
What are the four processess that occur in septicaemia?
- Capillary leak - albumin and other plasma proteins lead to hypovolaemia
- Coagulopathy - leads to bleeding and thrombosis, endothelial injury results in platelet release reactions, the protein C pathway and plasma anticoagulants are affected
- Metabolic derangement - particularly acidosis
- Myocardial failure - and multi-organ failure
This is why you dont do lumbar pucture - they’ll bleed out
Outline the presentation of TB meningitis.
- Similar presentation to bacterial meningitis but much longer to present (weeks instead of days)
- More likely to involve brain and cause neurological changes
- Tends to occur in immunocompromised patients
- No rash
List some complications of TB meningitis.
- Tuberculous granulomas
- Tuberculous abscesses
- Cerebritis
What is a typical MRI feature of TB meningitis?
Leptomeningeal enhancement
(arachnoid and pia mater appear brighter)
What is the most common infections of the CNS?
Aseptic meningitis (aseptic = negative CSF bacterial cultures)
What are the most common causative organisms in aseptic meningitis?
Enteroviruses:
- Coxsackie group B viruses
- Echoviruses
Which age group is susceptible to aseptic meningitis?
< 1 year
NOTE: normally self-resolving after 1-2 weeks
List some viruses that cause encephalitis.
- Herpes virus 1 (MOST COMMON)
- Mumps
- Measles
- Enteroviruses
What is becoming a leading cause of encephalitis worldwide?
West Nile virus
NOTE: this is transmitted by mosquitoes and birds
How is West nile in the UK
Infects birds
Birds migrate
Affects southern europe
people go on holiday
Which bacterium is associated with causing encephalitis?
Listeria monocytogenes
Name two types of amoeba that cause encephalitis.
- Naegleria fowleri
- Acanthamoeba species and Balamuthia mandrillaris
NOTE: these amoebae spread by direct extension (e.g. through the cribiform plates)
up your nose - swimming in the baths of bath
still, stagnant water
What is toxoplasmosis and how is it spread?
- Obligate intracellular parasite
- Spread via oral, transplacental or organ transplant route
How do bacteria that cause brain abscesses tend to spread?
Direct extension
(e.g. from otitis media, mastoiditis or paranasal sinuses)
List some organisms that can cause brain abscesses.
- Staphylococci
- Streptococci
- Gram-negative organisms (mainly in neonates)
- TB
- Actinomyces and Nocardia species
Name a common spinal infection.
Pyogenic vertebral osteomyelitis
How can pyogenic vertebral osteomyelitis spread?
Direct open spinal trauma from infections in adjacent structures
What are some long-term consequences of pyogenic vertebral osteomyelitis?
- Permanent neurologic defects
- Significant spinal deformity
- Death
List some risk factors for pyogenic vertebral osteomyelitis.
- Age
- IVDU - staph aureus
- Long-term systemic steroids
- Diabetes mellitus
- Organ transplantation
- Cancer
- Malnutrition
Compare the use of MRI and CT in CNS infections.
MRI is better than CT at detecting parenchymal abnormalities such as abscesses and infarctions
CT can be useful for looking at raised ICP
List some other useful tests for suspected meningitis.
- Blood culture - typical
- Blood PCR - aseptic
- Throat swab - Meningococus, Strep. Pneumo
Strep Pneumo (1in5) and Meningococcus (1in20) carried in nasopharynx
What studies can be done with CSF?
- Colour/clarity
- Cell counts
- Chemistry (protein and glucose)
- Stains (Gram, auramine, Inda Ink etc.)
- Cultures
- PCR
Describe the typical CSF analysis results of:
- Bacterial meningitis
- Aseptic meningitis
- Tuberculous meningitis
Bacterial meningitis:
- Turbid
- High polymorphs
- High protein
- Low glucose
Aseptic meningitis:
- Clear
- High lymphocytes
- High protein
- Normal glucose
Tuberculous meningitis:
- Clear
- High lymphocytes
- High protein
- Low glucose
Abnormal WCC in CSF >5
Describe the Gram-stain and microscopic appearance of:
- S. pneumonia
- N.meningitidis
- L. monocytogenes
- TB
- Cryptococcus
- S. pneumonia = Gram-positive alpha-haemolytic diplococci
- N.meningitidis = Gram-negative non-haemolytic diplococci
- L. monocytogenes = Gram-positive rods
- TB = Stains positively with Ziehl-Neelsen (red and blue)
-
Cryptococcus = Stains positively with India Ink (appears like an orbit - yeast in the middle with a capsule around the outside)
Does not gram stain
What is another key clinical feature of Cryptococcal meningitis?
High opening pressure
List some limitations of diagnositcs in menigitis.
- MRI oedema pattern may not differentiate between tumour or stroke or vasculitis in some patients
- Serology may not be useful in the early stages of infection
- Difficulties obtaining CSF
- PCR techniques are expensive
What is the generic therapy used in meningitis?
- Ceftriaxone 2g IV BD
- If > 50 years or immunocompromised = amoxicillin 2 g IV 4 hourly
NOTE: this is because ceftriaxone does NOT cover Listeria
What it the generic therapy used in meningo-encephalitis?
- Aciclovir 10 mg/kg IV TDS
- Ceftriazone 2 g IV BD
- If > 50 years or immunocompromised = amoxicillin 2 g IV 4 hourly
Name the specific therapy for meningitis caused by:
- S. pneumoniae
- N. meningitidis
- H. influenzae
- Group B Streptococcus
- Listeria
- Gram-negative bacilli
- Pseudomonas
1. S. pneumoniae = Ceftriaxone
2. N. meningitidis = Ceftriazone 4 g/day
3. H. influenzae = Cefotaxime 12 g/day
4. Group B Streptococcus = Pen G 18-24 mu/day
5. Listeria = Ampicillin 12 g/day
6. Gram-negative bacilli = Cefotaxime 12 g/day
7. Pseudomonas = Meropenem 6 g/day
