MI: CNS Infections and Meningitis Flashcards
What are the routes of entry into the CNS?
- Haematogenous (e.g. pneumococcus, meningococcus)
- Direct implantation (e.g. trauma or iatrogenic)
- Local extension (e.g. from the ear)
- PNS into CNS (e.g. rabies)
What is the most common route of entry for pathogens?
Haematogenous
What are the 4 main clinical syndromes caused by pathogens which successfully invade the CNS
- Meningitis (meninges)
- Encephalitis (brain)
- Myelitis (spinal cord)
- Neurotoxin (CNS and PNS)
Define Meningitis
inflammatory of the meninges and CSF
(Meningoencephalitis = infalmmation of teh meninges and brain parenchyma)
How is neurological damage caused 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)
- Chronic (days to weeks)
- Aseptic (caused by viruses so there is no pus)
Name three organisms that cause acute meningitis.
- Neisseria meningitidis
- Streptococcus pneumoniae (bimodal distrubution)
- Haemophilus influenzae
How many serotypes of N. meningitidis are there?
- ≥12 serotypes (90% = A, B, C)
A, B, C, W and Y are vaccinated against
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
What types of rashes can children develop if infected by N. Meningitidis
Resulting in:
* non-blanching rash (80% of children)
* Maculopapular rash (13% of children)
* No rash (7%)
How long does N. meningitidis take to cause infection?
< 10 days
50% will develop meningitis
7-10% will develop septicaemia
40% will develop both
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 deragnement - particularly acidosis
- Myocardial failure - and multi-organ failure
List some other, rarer bacterial causes of acute meningitis.
- Listeria monocytogenes
- Group B Streptococcus
- Escherichia coli
Outline the presentaiton of TB meningitis.
- TB meningitis is a type of chronic meningitis as takes weeks to present
- Similar presentation to acute meningitis
- Tends to occur in immunocompromised patients
- Involves the meninges and basal cisterns of the brain and spinal cord - as is the case with most chronic meningitis cases.
List some complications of TB meningitis.
- Tuberculous granulomas
- Tuberculous abscesses
- Cerebritis
What is a typical CT/MRI feature of TB meningitis?
Thickening of meninges and basal cisterns of brain and spinal cord
Dilatation of ventricles
What is the most common infections of the CNS?
Aseptic meningitis
What is aseptic meningitis?
Meningitis that is caused by viruses and is not purulent
What are the most common causative organisms in aseptic meningitis?
Coxsackie group B viruses
Echoviruses (HSV-2 commonest in UK)
Clinical Presentation of Aseptic meningitis
Commonly affected age group: < 1 year
- Non-specific rash accompanying headache, stiff neck, photophobia sx, buldging fontanelle
- normally self-resolving after 1-2 weeks
How is encephalitis transmitted?
Haematogenous (either person-to-person or through vectors such as mosquitoes)
List some viruses that cause encephalitis.
- Mumps
- Measles
- Enteroviruses
- Herpes viruses
What is becoming a leading cause of encephalitis worldwide?
West Nile virus
NOTE: this is transmitted by mosquitoes and birds
Which bacterium is associated with causing encephalitis?
Listeria monocytogenes
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.
- Streptococci
- Staphylococci
- Gram-negative organisms (mainly in neonates)
- TB, Fungi, Parasites
note in order of commonest
How can brain abscesses result in death
Pressure-related issues
Name a common spinal infection.
Pyogenic vertebral osteomyelitis - a common vertebral infection (e.g. staph or strep)
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 if left untreated?
- Permanent neurologic defects
- Significant spinal deformity
- Death
List some risk factors for pyogenic vertebral osteomyelitis.
- Age
- IVDU
- 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
List some other useful tests for suspected meningitis.
- CSF Study
- Blood culture
- Throat swab
- Blood PCR
- Sputum culture
- Urine culture
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
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)
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 treatment for anyone with suspected meningitis?
- Ceftriaxone 2g IV BD
- If > 50 years or immunocompromised or neonate= amoxicillin 2 g IV 4 hourly
NOTE: this is because ceftriaxone does NOT cover Listeria
What is the treatment for anyone with suspected meningo-encephalitis?
- Aciclovir 10 mg/kg IV TDS
- Ceftriaxone 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 = Pen G 18-24 mu/day
2. N. meningitidis = Ceftriaxone 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
