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YR5 Microbiology > CNS Infections and Meningitis > Flashcards

CNS Infections and Meningitis Flashcards

1
Q

What are the 4 modes to entry for CNS infections?

A
  • Haematogenous spread
  • Direct implantation - via instrumentation
  • Local extension - secondary to established infections
  • PNS into CNS
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2
Q

Most frequent route of entry for pathogens causing CNS infections?

A

Haematogenous

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3
Q

What is meningitis?
Region inflamed
Signs + Sx
Causative agents

A

Inflamed: Meninges + CSF

Signs + Sx: Fever, headache, stiff neck, usually some disturbance of brain function.

Causative agents: Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae, TB, Various viruses, Cryptococcus neoformans

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4
Q

What is encephalitis?
Region inflamed
Signs + Sx
Causative agents

A

Inflamed: Brain parenchyma

Signs + Sx: Disturbance of brain function

Causative agents: Rabies virus, arboviruses, Trypanosoma species, Prions, Amoeba.

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5
Q

What is myelitis?
Region inflamed
Signs + Sx
Causative agents

A

Inflamed: Spinal cord

Signs + Sx: Disturbance of nerve transmission

Causative agents: Poliovirus

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6
Q

What is neurotoxin?
Region inflamed
Signs + Sx
Causative agents

A

Inflamed: CNS + PNS

Signs + Sx: Paralysis, rigid (tetanus) or flaccid (botulism)

Causative agents: Clostridium tetani, Clostridium botulinum

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7
Q

What is meningoencephalitis?

A

Inflammation of meninges + brain parenchyma

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8
Q

How does meningitis cause neurological damage?

A
  • Direct bacterial toxicity.
  • Indirect inflammatory process + cytokine release + oedema.
  • Shock, seizures, + cerebral hypoperfusion.
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9
Q

What is the prognosis of meningitis?

A

Mortality ~ 10%

Morbidity ~ 5% neurological sequelae, mainly sensorineural deafness

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10
Q

What are the three classifications of meningitis? What are the usual causative organisms?

A
  • Acute: bacterial
  • Chronic: TB, Spherocytes, Cryptococcus
  • Aseptic: acute viral
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11
Q

What are 8 signs and symptoms of meningitis?

A
  • Vomiting
  • Fever
  • Headache
  • Stiff neck
  • Light aversion
  • Drowsiness
  • Joint pain
  • Fitting
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12
Q

What are the 6 most common causes of acute meningitis?

A
  • Neisseria meningitidis
  • Streptococcus pneumoniae
  • Haemophilus influenzae
  • Listeria monocytogenes
  • Group B Streptococcus
  • Escherichia coli
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13
Q

Which organism causes meningococcal meningitis?

A

Neiserria Meningitidis

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14
Q

Which organism causes pneumococcal meningitis?

A

Streptococcus penumoniae

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15
Q

What are the 3 most common causes of meningitis in the neonate (4w)?

A

Group B Streptococcus
Escherichia coli
Listeria monocytogenes

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16
Q

What are the 3 most common causes of meningitis in children/ young adults?

A

Neiserria Meningitidis
Haemophilus influenzae (rare in vaccinated countries)
Streptococcus pneumoniae

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17
Q

What are the 3 most common causes of meningitis in over 50s?

A

Neiserria Meningitidis
Streptococcus pneumoniae
Listeria monocytogenes

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18
Q

What are features of infection with N. Meningitidis?

A

Infectious cause of childhood death in all countries.

Transmission is person-to-person, from asymptomatic carriers.
Through nasopharyngeal mucosa in a susceptible individual

Pathogenic strains are found in only 1% of carriers.

Cause infections in <10d

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19
Q

What is a classical feature of meningococcal meningitis?

A

Nonblanching rash (petechial or purpuric) develops in 80% of children.

A maculopapular rash remains in 13% of children

No rash occurs in 7%.

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20
Q

When do cases of N.meningitidis peak? What vaccines are available?

A

Winter
A, C, Y + W135

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21
Q

What are links between meningitis and septicaemia in those with N. meningitidis?

A
  • 50% of cases have meningitis
  • 7-10% have septicemia
  • 40% have septicemia AND meningitis
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22
Q

Why is the clinical difference between meningitis and septicaemia important?

A

Patients who present with shock are treated differently than patients who present primarily with increased intracranial pressure (ICP).
Meningitis: LP indicated
Septicaemia with a bleeding diathesis + clotting deranged: LP CONTRAINDICATED

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23
Q

Which 4 processes produce the clinical spectrum of septicaemia?

A

Capillary leak: Albumin + other plasma proteins leads to hypovolemia.

Coagulopathy: Leads to bleeding + thrombosis.
* Endothelial injury results in platelet-release reactions
* The protein C pathway.
* Plasma anticoagulants.

Metabolic derangement: Particularly acidosis

Myocardial failue: + multi-organ failure.

24
Q

What is present on the CT scan of a patient with TB meningitis?

A

Enhancement in the basal cistern + meninges, with dilatation of the ventricles.

25
Q

Give 5 features of chronic tuberculosis meningitis?

A

Incidence: 544 per 100,000 pop. in Africa.

More common in immunosuppressed.

Mortality: 5.5 per 100,000

Involves the meninges + basal cisterns of the brain + spinal cord.

Can result in tuberculous granulomas, tuberculous abscesses, or cerebritis.

26
Q

What does a tuberculosis abscess look like on a CT head?

A

Enhancing thick-walled abscess.

27
Q

What are 6 features of aseptic meningitis?

A

Most common infection of the CNS.

Patients with aseptic meningitis have headache, stiff neck, + photophobia.

A nonspecific rash can accompany these Sx

Enteroviruses: Coxsackievirus group B + echoviruses are responsible for 80-90% cases in which a causative organism of aseptic meningitis is identified.

Most frequently occurs in <1y/o

Clinical course is self-limited + resolves in 1-2w.

28
Q

How is encephalitis transmitted?

A

Transmission is commonly either person to person, or through vectors:

  • Mosquitoes
  • Lice
  • Ticks
29
Q

What are some causative organisms of encephalitis?

A

Various viridae from Togavirus, Flavivirus, + Bunyavirus families.

But, West Nile Virus is becoming a leading cause of encephalitis internationally.

30
Q

What are 4 non viral causes of encephalitis?

A

Bacterial encephalitis:
* Listeria monocytogenes

Amoebic encephalitis:
* Naegleria fowleri: Habitat – warm water
* Acanthamoeba species, + Balamuthia mandrillaris: Brain abscess, aseptic or chronic meningitis.

31
Q

What is a parasitic cause of encephalitis? How is it transmitted? How does it manifest?

A

Toxoplasmosis

Obligate intracellular protozoal parasite, Toxoplasma gondii.

Via oral, transplacental route or organ transplantation.

Severe infection in immunocompromised patients.

Affected organs inc. gray + white matter of brain, retinas, alveolar lining of the lungs, heart, + skeletal muscle.

32
Q

What is full of toxoplasma gondii?

A

Kitten poo

33
Q

From which 5 conditions/ sites can infection spread to cause a brain abscesses?

A
  • Otitis media
  • Mastoiditis
  • Paranasal sinuses
  • Endocarditis
  • Haematogenously
34
Q

What are 7 causative organisms of a brain abscess?

A
  • Streptococci (both aerobic + anaerobic)
  • Staphylococci
  • Gram -ve organisms (esp in neonates)
  • Mycobacterium tuberculosis
  • Fungi
  • Parasites
  • Actinomyces + Nocardia species
35
Q

What can cause spinal infections? What may this lead to if left untreated?

A

Pyogenic vertebral osteomyelitis is a common form of vertebral infection.

Direct open spinal trauma, from infections in adjacent structures, from hematogenous spread of bacteria to a vertebra.

Untreated: permanent neurologic deficits, significant spinal deformity, or death.

36
Q

What are 7 risk factors of spinal infections?

A
  • Advanced age
  • Intravenous drug use
  • Long-term systemic steroids
  • Diabetes mellitus
  • Organ transplantation
  • Malnutrition
  • Cancer
37
Q

What are investigations for CNS infections?

A

MRI is superior to CT scanning in detecting parenchymal abnormalities e.g abscesses + infarctions.

CNS infections:
* CSF sample
* Brain tissue

Blood culture
Blood PCR
Throat swab

38
Q

What does this CSF study represent?

Appearance: Clear

Cells x 106/l: 0-5 leukocytes

Gram stain: Negative

Protein g/l: 0.15-0.4

Glucose mmol/l: >60% blood glucose level

A

Normal

39
Q

What does this CSF study represent?

Appearance: Turbid

Cells x 106/l: 100-2000 polymorphs

Gram stain: Positive results

Protein g/l: 0.5-4.0

Glucose mmol/l: <60% blood glucose level

A

Purulent meningitis
Polymorphic nuclei in neutrophils indicate bacterial cause

DDx:

Bacterial meningitis
* ?Meningococcus
* ?Pneumococcus
* ?Listeria

40
Q

What does this CSF study represent?

Appearance: Clear or slightly turbid

Cells x 106/l: 15-500 lymphocytes

Gram stain: Negative

Protein g/l: 0.5-1.0

Glucose mmol/l: >60% blood glucose level

A

Aseptic meningitis

DDx:

  • Viral meningitis
  • Partially abx treated bacterial meningitis
  • Encephalitis
  • Brain abscess
  • TB/fungal meningitis
41
Q

What does this CSF study represent?

Appearance: Clear or slightly turbid

Cells x 106/l: 30-500 lymphocytes or some polymorphs

Gram stain: Negative

Protein g/l: 1.0-6.0

Glucose mmol/l: <60% blood glucose level

A

Tuberculosis meningitis

DDx:

  • TB meningitis
  • Brain abscess
  • Cryptococcal meningitis
42
Q

A 20 year old woman presents with headache and neck stiffness. What is the causative pathogen?

A

Gram positive cocci

Pneumococcus

43
Q

A 18 year old man present with headache and neck stiffness. What is the causative pathogen?

A

Gram negative cocci

Meningococcus

44
Q

A 65 year old presents with headache and neck stiffness. What is the causative pathogen?

A

Gram positive rod

Listeria

45
Q

A 45 year old presents with headache and neck stiffness. What is the causative pathogen?

A

Ziehl-Neelsen stain

TB

46
Q

A 35 year old HIV+ man presents with headache and neck stiffness. What is the causative pathogen?

A

Indian ink stains

Cryptococcus

47
Q

What are 6 limitations of diagnostics in CNS infections?

A

MRI oedema pattern + moderate mass effect cannot be differentiated from tumor/ stroke/ vasculitis in some patients.

Infections in early stages + serological tests.

Amount of CSF.

PCR techniques.

Methods to detect amoebic infections.

Availability of good laboratory technique.

48
Q

What is the management of meningitis?

A

Ceftriaxone 2g IV bd

If >50y or immunocompromised add:
Amoxicillin 2g IV 4 hourly

49
Q

What is the management of meningoencephalitis?

A

Aciclovir 10mg/kg IV tds

Ceftriaxone 2g IV bd

If >50y or immunocompromised add:
Amoxicillin 2g IV 4hourly

50
Q

What is the recommended therapy for S. Pneumoniae or N. Meningitidis?

A

Pen G 18-24 mu/d
or
Ampicillin 12 g/d
or
Ceftriaxone 4 g/d
or
Chloro 75-100 mg/kg/d

51
Q

What is the recommended therapy for H. Influenzae?

A

Cefotaxime 12 g/d
or
Ceftriaxone 4 g/d

52
Q

What is the recommended therapy for Group B Strep?

A

Pen G
or
Amoxicillin [plus aminoglycoside]

53
Q

What is the recommended therapy for Listeria?

A

Amoxicillin 12 g/d [plus aminoglycoside]

54
Q

What is the recommended therapy for Gram negative bacilli?

A

Cefotaxime 12 g/d
or
Ceftriaxone 4g/d

55
Q

What is the recommended therapy for Pseudomonas?

A

Meropenem 6g/d
or
Ceftazidime 6g/d

56
Q

What is the most common cause of encephalitis in the UK?

A

HSV-2

YR5 Microbiology (23 decks)

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