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PATH FINAL > MI: CNS Infections and Meningitis > Flashcards

MI: CNS Infections and Meningitis Flashcards

1
Q

What are the routes of entry into the CNS?

A
  • 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)
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2
Q

What is the most common route of entry for pathogens?

A

Haematogenous

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3
Q

What are the 4 main clinical syndromes caused by pathogens which successfully invade the CNS

A
  • Meningitis (meninges)
  • Encephalitis (brain)
  • Myelitis (spinal cord)
  • Neurotoxin (CNS and PNS)
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4
Q

Define Meningitis

A

inflammatory of the meninges and CSF

(Meningoencephalitis = infalmmation of teh meninges and brain parenchyma)

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5
Q

How is neurological damage caused in meningitis

A
  • Direct bacterial toxicity
  • Indirect inflammatory response, cytokine release and oedema
  • Shock, seizures and cerebral hypoperfusion
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6
Q

What are the three types of meningitis?

A
  • Acute (hours to days)
  • Chronic (days to weeks)
  • Aseptic (caused by viruses so there is no pus)
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7
Q

Name three organisms that cause acute meningitis.

A
  • Neisseria meningitidis
  • Streptococcus pneumoniae (bimodal distrubution)
  • Haemophilus influenzae
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8
Q

How many serotypes of N. meningitidis are there?

A
  • ≥12 serotypes (90% = A, B, C)

A, B, C, W and Y are vaccinated against

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9
Q

How does N. meningitidis enter the body?

A

Through the nasopharyngeal mucosa in susceptible individuals

NOTE: only 1% of carriers of N. meningitidis have pathogenic strains

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10
Q

What types of rashes can children develop if infected by N. Meningitidis

A

Resulting in:
* non-blanching rash (80% of children)
* Maculopapular rash (13% of children)
* No rash (7%)

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11
Q

How long does N. meningitidis take to cause infection?

A

< 10 days

50% will develop meningitis
7-10% will develop septicaemia
40% will develop both

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12
Q

What are the four processess that occur in septicaemia?

A
  • 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
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13
Q

List some other, rarer bacterial causes of acute meningitis.

A
  • Listeria monocytogenes
  • Group B Streptococcus
  • Escherichia coli
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14
Q

Outline the presentaiton of TB meningitis.

A
  • 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.
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15
Q

List some complications of TB meningitis.

A
  • Tuberculous granulomas
  • Tuberculous abscesses
  • Cerebritis
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16
Q

What is a typical CT/MRI feature of TB meningitis?

A

Thickening of meninges and basal cisterns of brain and spinal cord

Dilatation of ventricles

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17
Q

What is the most common infections of the CNS?

A

Aseptic meningitis

18
Q

What is aseptic meningitis?

A

Meningitis that is caused by viruses and is not purulent

19
Q

What are the most common causative organisms in aseptic meningitis?

A

Coxsackie group B viruses

Echoviruses (HSV-2 commonest in UK)

20
Q

Clinical Presentation of Aseptic meningitis

A

Commonly affected age group: < 1 year

  • Non-specific rash accompanying headache, stiff neck, photophobia sx, buldging fontanelle
  • normally self-resolving after 1-2 weeks
21
Q

How is encephalitis transmitted?

A

Haematogenous (either person-to-person or through vectors such as mosquitoes)

22
Q

List some viruses that cause encephalitis.

A
  • Mumps
  • Measles
  • Enteroviruses
  • Herpes viruses
23
Q

What is becoming a leading cause of encephalitis worldwide?

A

West Nile virus

NOTE: this is transmitted by mosquitoes and birds

24
Q

Which bacterium is associated with causing encephalitis?

A

Listeria monocytogenes

25
Q

What is toxoplasmosis and how is it spread?

A
  • Obligate intracellular parasite
  • Spread via oral, transplacental or organ transplant route
26
Q

How do bacteria that cause brain abscesses tend to spread?

A

Direct extension (e.g. from otitis media, mastoiditis or paranasal sinuses)

27
Q

List some organisms that can cause brain abscesses.

A
  • Streptococci
  • Staphylococci
  • Gram-negative organisms (mainly in neonates)
  • TB, Fungi, Parasites

note in order of commonest

28
Q

How can brain abscesses result in death

A

Pressure-related issues

29
Q

Name a common spinal infection.

A

Pyogenic vertebral osteomyelitis - a common vertebral infection (e.g. staph or strep)

30
Q

How can pyogenic vertebral osteomyelitis spread?

A

Direct open spinal trauma from infections in adjacent structures

31
Q

What are some long-term consequences of pyogenic vertebral osteomyelitis if left untreated?

A
  • Permanent neurologic defects
  • Significant spinal deformity
  • Death
32
Q

List some risk factors for pyogenic vertebral osteomyelitis.

A
  • Age
  • IVDU
  • Long-term systemic steroids
  • Diabetes mellitus
  • Organ transplantation
  • Cancer
  • Malnutrition
33
Q

Compare the use of MRI and CT in CNS infections.

A

MRI is better than CT at detecting parenchymal abnormalities such as abscesses and infarctions

34
Q

List some other useful tests for suspected meningitis.

A
  • CSF Study
  • Blood culture
  • Throat swab
  • Blood PCR
  • Sputum culture
  • Urine culture
35
Q

What studies can be done with CSF?

A
  • Colour/clarity
  • Cell counts
  • Chemistry (protein and glucose)
  • Stains (Gram, auramine, Inda Ink etc.)
  • Cultures
  • PCR
36
Q

Describe the typical CSF analysis results of:

  1. Bacterial meningitis
  2. Aseptic meningitis
  3. Tuberculous meningitis
A

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
37
Q

Describe the Gram-stain and microscopic appearance of:

  1. S. pneumonia
  2. N.meningitidis
  3. L. monocytogenes
  4. TB
  5. Cryptococcus
A
  1. S. pneumonia = Gram-positive alpha-haemolytic diplococci
  2. N.meningitidis = Gram-negative non-haemolytic diplococci
  3. L. monocytogenes = Gram-positive rods
  4. TB = Stains positively with Ziehl-Neelsen (red and blue)
  5. Cryptococcus = Stains positively with India Ink (appears like an orbit - yeast in the middle with a capsule around the outside)
38
Q

What is another key clinical feature of Cryptococcal meningitis?

A

High opening pressure

39
Q

List some limitations of diagnositcs in menigitis.

A
  • 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
40
Q

What is the treatment for anyone with suspected meningitis?

A
  • 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

41
Q

What is the treatment for anyone with suspected meningo-encephalitis?

A
  • Aciclovir 10 mg/kg IV TDS
  • Ceftriaxone 2 g IV BD
  • If > 50 years or immunocompromised = amoxicillin 2 g IV 4 hourly
42
Q

Name the specific therapy for meningitis caused by:

  1. S. pneumoniae
  2. N. meningitidis
  3. H. influenzae
  4. Group B Streptococcus
  5. Listeria
  6. Gram-negative bacilli
  7. Pseudomonas
A

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

PATH FINAL (36 decks)

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