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Arjun's PM copy-Microbiology and Infection > 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
  • Direct implantation
  • Local extension
  • PNS into CNS (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 is aseptic meningitis?

A

Meningitis that is caused by viruses and is not purulent

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4
Q

What are the causes of neurological damage in meningitis

A
  • Direct bacterial toxicity
  • Indirect inflammatory response, cytokine release and oedema
  • Shock, seizures and cerebral hypoperfusion
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5
Q

What are the three types of meningitis?

A
  • Acute (hours to days) - bacterial
  • Chronic (days to weeks) - TB and weird
  • Aseptic (caused by viruses so there is no pus)
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6
Q

Name three organisms that cause acute meningitis.

A
  • Neisseria meningitidis
  • Streptococcus pneumoniae
  • Haemophilus influenzae
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7
Q

How many serotypes of N. meningitidis are there?

A

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

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8
Q

List some other, rarer bacterial causes of acute meningitis.

A
  • Listeria monocytogenes
  • Group B Streptococcus
  • Escherichia coli
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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

How long does N. meningitidis take to cause infection?

A

< 10 days

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11
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 derangement - particularly acidosis
  • Myocardial failure - and multi-organ failure

This is why you dont do lumbar pucture - they’ll bleed out

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12
Q

Outline the presentation of TB meningitis.

A
  • 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
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13
Q

List some complications of TB meningitis.

A
  • Tuberculous granulomas
  • Tuberculous abscesses
  • Cerebritis
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14
Q

What is a typical MRI feature of TB meningitis?

A

Leptomeningeal enhancement
(arachnoid and pia mater appear brighter)

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15
Q

What is the most common infections of the CNS?

A

Aseptic meningitis (aseptic = negative CSF bacterial cultures)

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16
Q

What are the most common causative organisms in aseptic meningitis?

A

Enteroviruses:

  • Coxsackie group B viruses
  • Echoviruses
17
Q

Which age group is susceptible to aseptic meningitis?

A

< 1 year

NOTE: normally self-resolving after 1-2 weeks

18
Q

List some viruses that cause encephalitis.

A
  • Herpes virus 1 (MOST COMMON)
  • Mumps
  • Measles
  • Enteroviruses
19
Q

What is becoming a leading cause of encephalitis worldwide?

A

West Nile virus

NOTE: this is transmitted by mosquitoes and birds

20
Q

How is West nile in the UK

A

Infects birds
Birds migrate
Affects southern europe
people go on holiday

21
Q

Which bacterium is associated with causing encephalitis?

A

Listeria monocytogenes

22
Q

Name two types of amoeba that cause encephalitis.

A
  • 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

23
Q

What is toxoplasmosis and how is it spread?

A
  • Obligate intracellular parasite
  • Spread via oral, transplacental or organ transplant route
24
Q

How do bacteria that cause brain abscesses tend to spread?

A

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

25
Q

List some organisms that can cause brain abscesses.

A
  • Staphylococci
  • Streptococci
  • Gram-negative organisms (mainly in neonates)
  • TB
  • Actinomyces and Nocardia species
26
Q

Name a common spinal infection.

A

Pyogenic vertebral osteomyelitis

27
Q

How can pyogenic vertebral osteomyelitis spread?

A

Direct open spinal trauma from infections in adjacent structures

28
Q

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

A
  • Permanent neurologic defects
  • Significant spinal deformity
  • Death
29
Q

List some risk factors for pyogenic vertebral osteomyelitis.

A
  • Age
  • IVDU - staph aureus
  • Long-term systemic steroids
  • Diabetes mellitus
  • Organ transplantation
  • Cancer
  • Malnutrition
30
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

CT can be useful for looking at raised ICP

31
Q

List some other useful tests for suspected meningitis.

A
  • Blood culture - typical
  • Blood PCR - aseptic
  • Throat swab - Meningococus, Strep. Pneumo

Strep Pneumo (1in5) and Meningococcus (1in20) carried in nasopharynx

32
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
33
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

Abnormal WCC in CSF >5

34
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)
    Does not gram stain
35
Q

What is another key clinical feature of Cryptococcal meningitis?

A

High opening pressure

36
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
37
Q

What is the generic therapy used in meningitis?

A
  • Ceftriaxone 2g IV BD
  • If > 50 years or immunocompromised = amoxicillin 2 g IV 4 hourly

NOTE: this is because ceftriaxone does NOT cover Listeria

38
Q

What it the generic therapy used in meningo-encephalitis?

A
  • Aciclovir 10 mg/kg IV TDS
  • Ceftriazone 2 g IV BD
  • If > 50 years or immunocompromised = amoxicillin 2 g IV 4 hourly
39
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 = 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

Arjun's PM copy-Microbiology and Infection (26 decks)

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