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a path 3 > MICRO: CNS infections and meningitis > Flashcards

MICRO: CNS infections and meningitis Flashcards

1
Q

What are the 4 routes of pathogen entry into the CNS? What is the most common route of entry?

A

Routes of Pathogen Entry into the CNS – 4 routes of entry…

  • Haematogenous (e.g. pneumococcus, meningococcus carriage may penetrate and seed) - MOST COMMON
  • Direct implantation (e.g. trauma)
  • Local extension (e.g. from the ear like swimmer’s ear)
  • PNS into CNS (e.g. rabies after bite)
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2
Q

What is meningtitis? Its signs and symptoms? Its causative agents?

A
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3
Q

What is encephalitis? Its signs and symptoms? Its causative agents?

A
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4
Q

What is myelitis? Its signs and symptoms? Its causative agents?

A
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5
Q

What does neurotoxin infection affect? Its signs and symptoms? Its causative agents?

A
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6
Q

What is meningoencephalitis?

A

inflammation of the meninges and brain parenchyma

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7
Q

What is neurological damage caused by in meningitis? How common is it?

A

Neurological damage = 10% mortality, 5% neurological sequelae; sensorineural deafness)

Caused by:

  1. Direct bacterial toxicity
  2. Indirect inflammatory process and cytokine release and oedema (n.b. tight space, oedema = bad)
  3. Shock, seizures and cerebral hypoperfusion
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8
Q

How can you classify CNS infections?

A
  • Classification:
    1. Acute (hours to days) - usually bacterial meningitis
    2. Chronic (days to weeks) - usually TB
    3. Aseptic (caused by viruses so there is no pus) - usually viral
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9
Q

In which group would you classify meningococcal meningitis?

A

Acute

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10
Q

What are the main 3 causes of acute meningitis?

A
  1. Neisseria meningitidis
  2. Streptococcus penumoniae
  3. Haemophilus influenzae

Also:

  • Listeria
  • GBS
  • E.coli

Other causes below:

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11
Q

What are the other causes of meningitis in specific populations?

A
  1. Listeria monocytogenes - key cause of meningoencephalitis, old, pregnant,
  2. Group B Streptococcus - common in females, 1/3 of European women, can cause neonatal meningitis after birth
  3. Escherichia coli - biphasic in old people and neonates
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12
Q

What are the rash presentations in N. meningitidis?

A
  • Non-blanching rash (80% of children)
  • Maculopapular rash (13% of children)
  • No rash (7% of children)
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13
Q

What are the other phenotypes of N. meninitidis? Why is it important to distinguish?

A
  • 50% have meningitis,
  • 7-10% have septicaemia,
  • 40% have meningitis AND septicaemia
    • Important to distinguish as treatment for shock and raised ICP is different *
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14
Q

What four processes govern the clinical presentation of septicaemia?

A
  • Capillary Leak – albumin and other plasma proteins leads 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
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15
Q

How many serotypes of N meningitidis? How is it acquired?

A
  • ≥12 serotypes (90% = A, B, C); A, B, C, W and Y are vaccinated against
  • Transmitted from person-to-person, from asymptomatic carriers
    • Pathogenic strains are only found in about 1% of carriers
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16
Q

Give an examples of chronic meningitis.

A

Tuberculous chornic meningitis

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17
Q

What are the complications of tuberculous chronic meningitis?

A
  • Tuberculous granulomas
  • Tuberculous abscesses (i.e. enhancing thick-walled abscesses) in the brain
  • Cerebritis

Below: normal brain vs TB brain vs tuberculoma (leading to death)

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18
Q

How does tuberculous chronic meningitis present? What is the mortality?

A

Similar presentation to acute meningitis (fever, headache, neck stiffness) but lower mortality (0.000055%)

More common in immunosuppressed patients

Involves the meninges and basal cisterns of the brain and spinal cord with dilatation of ventricles

19
Q

What is the most common infection of the CNS?

A

Aseptic meningitis

20
Q

How does aseptic meningitis present? What are the two most common causes?

A
  • Presentation: headache, stiff neck, photophobia
  • A non-specific rash may accompany these symptoms

Organisms (80-90% of organisms) – VIRAL:

  • Enteroviruses - Coxsackie group B and Echoviruses
  • Herpes simples (1&2)
21
Q

Who is most affected by aseptic meningitis? What is the management?

A

Usually occurs in children <1 year

Self-limiting disease that resolves in 1-2 weeks

22
Q

Other than enteroviruses and herpes simplex, what are the other causes of meningitis?

A
23
Q

What are the main modes of transmission of encephalitis?

A

Transmission is pretty much ALL haematogenous:

  1. Person-to-person
  2. Vectors (e.g. mosquitoes, lice, ticks)
24
Q

Which virus is becoming a leading cause of encephalitis worldwide?

A

IMPORTANT: West Nile Virus is becoming a leading cause of encephalitis worldwide

  • Mainly transferred by mosquitoes and birds (European birds spend the winter in Southern Europe and Africa)
  • West Nile Virus has spread across the USA but hasn’t reached the UK yet
25
Q

What are the causes of non-viral encephalitis?

A
  • Bacterial – Listeria monocytogenes
  • Amoeba (spread by direct extension through cribriform plates):
    • Naegleria fowleri - habitat – warm water
    • Acanthamoeba spp. & Balamuthia mandrillaris - brain abscess, aseptic & chronic meningitis
  • Toxoplasmosis (obligate intracellular protozoal parasite – Toxoplasma gondii):
    • Spread via the faeco-oral, transplacental or organ transplant route
    • Causes severe infection in immunocompromised patients
    • Affected organs = grey & white matter of brain, retinas, alveolar lining of lungs, heart, skeletal muscle
26
Q

What is the pathophysiology of brain abscesses?

A
  • Cause death due to pressure-related issues
  • Pathophysiology:
    • Direct extension (e.g. otitis media, mastoiditis, para-nasal sinuses)
    • Occasionally spread haematogenously (e.g. endocarditis)
27
Q

What are the causative agents for brain abscesses?

A
  • Causative Organisms (Strep > Staph > gram -ve > other):
    • Streptococci (anaerobic and aerobic)
    • Staphylococci
    • Gram-negative organisms (mainly in neonates)
    • TB, fungi, parasites, actinomyces and Nocardia species
28
Q

How are spinal infections spread? What is a common type?

A
  • Pyogenic vertebral osteomyelitis is a common form of vertebral infection (e.g. staph and strep)
  • Spread via… direct open spinal trauma or it can spread haematogenously
29
Q

What are the complications of spinal infections?

A
  • Permanent neurological deficits
  • Significant spinal deformity
  • Death
30
Q

What are the risk factors for spinal infections?

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

(similar to those for getting endocarditis)

31
Q

What investigations should be done for CNS infections?

A
  1. MRI>CT
  2. If CNS affected:
    • CSF sample
    • brain tissue - but rarely done
  3. Blood culture - very important as usually haematogenous spread, relies on no antibiotics given
  4. Throat swab
  5. Blood PCR - good if antibiotics given
32
Q

Which imaging should be done to detect brain abscesses and infarctions?

A

Plain CT brain are useless at seeing brain abscesses

Enhancing lesions better seen on MRI BUT CT is more readily available

33
Q

Describe the normal, purulent, aseptic and TB meningitis CSF presentations in terms of

  • appearance
  • cells
  • gram stain/antigen tests
  • protein g/l
  • glucose mmol/l
  • main differential
A
34
Q
A

S pneumoniae because dark purple with gram stain which means gram positive

  • Arranged as diplococci*
  • NB: meningococci are gram -ve*
35
Q
A

Gram negative diplococci seen

Many neutrophils present

No haemolysis

N meningitidis

36
Q
A

Listeria monocytogenes

Gram positive rod

37
Q
A

M tuberculosis

Ziehl-Neelsen stain seen (red and blue)

38
Q
  • Hx: MSM, 3/7 history
  • High opening pressure on LP
A

Cryptococcus neoformans

  • HOP pathogenomic of C. neoformans
  • Occurs in immunocompromised people
  • India ink stain used
  • Cryptococcus is a yeast surrounded by capsule as shown
39
Q

What are the limitations of diagnostics?

A
  • MRI oedema pattern and moderate mass effect cannot be differentiated from tumour or stroke or vasculitis
  • Serology may not be useful in early stages of infection
  • Difficulties obtaining sufficient CSF
  • PCR techniques are expensive
  • Methods to detect amoebic infections
  • Availability of good laboratory technique
40
Q

If you suspect CNS infections, what should you do within:

  1. 30mins
  2. 1-2 hours
  3. 24-48 hours
A

Initial doses of antibiotics should be given almost immediately. This can be changed a bit later.

41
Q

What is the generic treatment for meningitis and meningo-encephalitis?

A
42
Q

Specific treatments for some CNS infections:

A
43
Q

Learn the appearance of these cells:

A
44
Q

List some adjunctive mangement steps for CNS infections.

A
  • Corticosteroids (do NOT give them without speaking to a specialist, but it can be useful for cerebral oedema)
  • Repeat LP
  • Public health – may need to be reported

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