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Meningitis Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

definition of meningitis?

A

•INFECTION OF BRAIN’S CONNECTIVE TISSUE COVERING

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2
Q

What is the most frequent route of entry for pathogens causing CNS infections ?

A

Haematogenous spread

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3
Q

what is meningitis

A

inflammatory process of the meninges and CSF
neurological damage caused by:
- direct bacterial toxicity
- indirect inflammatory processes and cytokine release
- shock, seizures and cerebral hypoperfusion

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4
Q

what are the symptoms of bacterial meningitis?

A
  • HEADACHE. FEVER. DROWSINESS/UNCONSCIOUSNESS.
  • ALSO, PHOTOPHOBIA, VOMITING
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5
Q

what are the signs of bacterial meningitis to look out for?

A
  • NECK/SPINE STIFFNESS
  • POSSIBLE RASH - DEPENDING ON AETIOLOGY
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6
Q

List 4 routes of entry to the CNS for pathogens

A
  • Haematogenous spread (meningococcus, pneumococcus)
  • Direct implantation (after surgery)
  • Local extension (from the ear)
  • PNS into CNS (rabies)
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7
Q

why is bacterial meningitis considered a medical emergency?

A
  • APPARENT HEALTH TO DEATH IN 24 HOURS
  • GREATER MORBIDITY THAN VIRAL
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8
Q

what is the prevalence of bacterial meningitis in the uk?

A
  • 2000 CASES BACTERIAL MENINGITIS PER YEAR IN UK
  • 150 DEATHS
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9
Q

differential diagnosis?

A
  • SUBARACHNOID HAEMORRHAGE. CEREBRAL ABSCESS
  • CEREBROSPINAL FLUID (CSF) FROM SUBARACHNOID HAEMORRHAGE
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10
Q

what is the colour of the CSF and why?

A

YELLOW/ORANGE COLOUR: STAINED BY LYSED RBC’s. = “XANTHOCHROMIA”

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11
Q

Which organisms is a common cause of neonatal meningitis ?

A

Group B streptococcus

Also Listeria monocytogenes

Floral bacteria in the mothers vagina or maternal bacteraemia

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12
Q

which organisms cause meningitis up to 5 years of age?

A

•Neisseria meningitidis.

Streptococcus pneumoniae.

Haemophilus influenzae (rare in UK).

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13
Q

which organisms cause meningitis from 5 years to 50 years of age?

A

Neisseria meningitidis.

Streptococcus pneumoniae.

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14
Q

which organisms cause meningitis above 50 years of age?

A

•Streptococcus pneumoniae.

Neisseria meningitidis.

Rarely: L. monocytogenes and TB

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15
Q

what are the predisposing factors for neonate disease?

A
  • LOW BIRTH WEIGHT (eg premature)
  • EARLY RUPTURE OF MEMBRANES
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16
Q

what is the key group of adults predisposed to infection?

A

immunocomprised

  • susceptible to many infections
  • yeasts, esp. Cryptococcus neoformans in AIDS
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17
Q

other predisposing factors?

A

•SINUSITIS,

MASTOIDITIS,

OTITIS MEDIA,

PNEUMONIA,

SKULL FRACTURE,

ALCOHOLISM

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18
Q

What organism commonly causes chronic meningitis ?

A

Tuberculosis

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19
Q

What organisms can cause aseptic meningitis ?

A

Enterovirus - coxsackievirus
Herpes simplex

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20
Q

What is aseptic meningitis?

A
  • also known as viral meningitis - no pus found
  • Usually acute viral meningitis
  • not as severe as bacterial
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21
Q

Which N.meningitidis serotypes are there vaccinations for ?

A

B and C

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22
Q

What type of meningitis is suggested by this CSF sample ? What are the likely causative organisms ?

CSF appearance: clear
Cells: 0-5 leukocytes
Gram stain/antigen tests: negative results
Protein: 0.15-0.4 g/l
Glucose: 2.2-3.3mmol/m

A

Normal

No organisms

**ADD TABLE FROM NOTES PLS**

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23
Q

What type of meningitis is suggested by this CSF sample ? What are the likely causative organisms ?

CSF appearance: Turbid
Cells: 100-2000 polymorphs
Gram stain/antigen tests: positive results
Protein: 0.5-3.0 g/l
Glucose: 0-2.2 mmol/l

A

Purulent meningitis (bacterial)

Meningococcus
Pneumococcus
Listeria

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24
Q

What type of meningitis is suggested by this CSF sample ? What are the likely causative organisms ?

CSF appearance: clear/slightly turbid
Cells: 30-500 lymphocytes/ some polymorphs
Gram stain/antigen tests: negative results (scanty acid fast bacilli)
Protein: 1.0-6.0 g/l (high)
Glucose: 0-2.2 (normal)

A

Tuberculous meningitis

Mycobacterium TB

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25
Q

Which imaging is best for detecting parenchymal abnormalities e.g. abscesses and infarctions?

Which is more commonly available and so used?

A

Best: MRI

More used: CT

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26
Q

Culture and microscopy shows a gram +ve, alpha haemolytic diplococcus organism, what is the likely organism causing the meningitis ?

A

Streptococcus. Pneumoniae

  • this is Gram POSITIVE a-haemolytic diplococcus
  • Gram positive = pneumococcus (diplococci) = Stains purple on gram stain (Positive = Purple)
  • Gram negative = meningococcus = Stains pink on gram stain
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27
Q

Culture and microscopy shows a gram -ve diplococci which is non-haemolytic, what organism is the likely cause of this meningitis ?

What would agar show?

A

Meningococcus (Neisseria meningitides) - gram NEGATIVE cocci

  • stains PINK

Agar would show lots of neutrophils

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28
Q

Culture and microscopy shows gram +ve purple rods, what organism is the likely cause of this meningitis ?

A

Listeria monocytogenes

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29
Q

A 45-year-old presents with headache and neck stiffness over a period of weeks. LP shows cuboidal structures that appear red against a blue stain. What is the causative pathogen?

A

TB

  • NB this happens over WEEKS (chronic meningitis cause)
  • This is Ziehl-Neelsen stain
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30
Q

India ink stain: shows orbit structures (yeast cells with surrounding halos)
Lumber puncture: high opening pressure
IN a patient with HIV

What is the likely causative organism of this meningitis ?

A

Cryptococcus Neoformans

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31
Q

Which organism commonly causes meningitis in men who have sex with men (MSM)

A

Cryptococcus Neoformans

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32
Q

Which drug is effective against Meningococcus, pneumococcus, haemophilus and e.coli ?

A

Ceftriaxone I.V

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33
Q

Which drug is effective at treating Listeria ?

A

Amoxicillin

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34
Q

Which organism is most commonly associated with recurrent aseptic meningitis (Mollaret’s meningitis) ?

A

HSV-1 and HSV-2

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35
Q

Which organisms are the most common cause of aseptic meningitis ?

A

Enterovirus (80%) - Echovirus, coxsackie virus

36
Q

common causes of myelitis

A

poiovirus

37
Q

common causes of neurotoxin release

A

clostridium tenani
clostridium botulinum

38
Q

list other causes of meningitis

A

listeria monocytogenes
group B strep
E. coli

rare:
TB, S. Aureus, T. Pallidum, cryptococcus neoformans

39
Q

describe the processes whereby septicaemia occurs

A
  • capillary leak - albumin and other plasma proteins lead to hypovolaemia
  • coagulopathy - leads to bleeding and thrombosis
  • metabolic derrangeent - acidosis
  • myocardial failure and multi-organ failure
40
Q

complications of TB meningitis

A
  • common in immunosuppressed
  • complications = tuberculosis granulomas
  • tuberculosis abscesses
  • cerebritis
  • there is leptomeningeal enhancement
41
Q

features of aseptic meningitis

A
  • most common infection of the CNS
  • coxsackie group B
  • echoviruses
  • usually in children <1 year
  • self-limiting, resolves in 1-2 weeks
42
Q

How to clinically differentiate encephalitis from meningitis

A

The disturbance of cognitive function in ecephalitis is what differentiates meningitis to encephalitis

43
Q

4 samples to send for Ix if meningitis suspected

A
  • CSF
  • Blood culture
  • Throat swab
  • Sputum culture
44
Q

What colour does gram positive stain?

A

Stains purple on gram stain (Positive= Purple)

  • e.g. Gram positive = pneumococcus (diplococci)
45
Q

What colour does gram negative stain?

A

Stains pink on gram stain e.g. meningicoccus)

46
Q

Which group tend to be infected more by listeria for meningitis? (2)

A
  • Old age (have age-related immunosenescence)
  • Immunosuppressed pts
47
Q

Most common infection of CNS

Which age group does it mainly affect?

How does it resolve?

A

Aseptic Meningitis (viral)

Mainly affects children < 1 year

Self-limiting condition (resolves over 1-2 weeks) - NO antivirals

48
Q

how can aseptic meningitis be treated?

A
  • Aciclovir for HSV meningitis
  • Other antivirals: not effective or not evaluated
49
Q

Which group of pts are mainly affected by chronic meningitis + what is common causative organism?

A
  • group: immunosuppressed + old
  • common organism: TB
50
Q

what is the key group of adults predisposed to infection?

A

immunocomprised

  • susceptible to many infections
  • yeasts, esp. Cryptococcus neoformans in AIDS
51
Q

what is CSF?

A

CEREBROSPINAL FLUID

52
Q

what is the cerebrospinal fluid?

A
  • Brain’s blood vessels
  • Very tight intercellular junction
  • Lack of pinocytosis
  • Forms the basis of the “Blood-Brain Barrier”
53
Q

what is the problem with the blood-brain barrier?

A
  • Has a protective function, but:
  • Results in low antibody and WBC levels in CSF
54
Q

what is the result if organisms do penetrate the barrier?

A

Are temporarily relatively protected from immune system

55
Q

normal CSF characteristics?

A

< 5 WBC’s/mm3 ~ 75% polymorphs,

20% lymphocytes

2/3 plasma glucose.

Clear. Sterile.

56
Q

CSF characteristics in bacterial meningitis?

A

1000 - 10000 WBC’s/mm3.

Increased polymorphs¯ glucose.

Turbid. +/- Visible organisms in smear

57
Q

CSF characteristics in aseptic meningitis?

A

50 - 1500 WBC’s/mm3.

Lymphocytes predominant

Normal glucose. Clear.

58
Q

CSF characteristics in tuberculous meningitis?

A

<1000 WBC’s/mm3.

Lymphocytes predominant

or normal glucose

59
Q

can CSF be used for diagnostics?

A

Useful sample - rapid diagnosis by microscopy

and PCR for genome detection

•Antigen detection using specific antisera

60
Q

does genome detection work for all

A
61
Q

how is sampled obtained?

A

obtained by lumbar puncture

Potentially dangerous to obtain

62
Q

what microscopy is used?

A

•Gram stain, WBC cell count, WBC differential count

63
Q

how is sample cultured?

A

Blood agar in 5% CO2

Chocolate agar in 5% CO2

Blood agar - anaerobic

Antibiotic sensitivity testing

64
Q

is it worth doing blood cultures?

A

yes

40% cases due to N. meningitidis and S. pneumoniae are positive

65
Q

what else about blood samples?

A
  • Whole blood more useful than serum
  • PCR for genome detection
66
Q

what other diagnostic tests are helpful?

A

rash biopsy and throat swab

for microscopy (rash biopsy), culture and antibiotic sensitivities

67
Q

MENINGOCOCCAL DISEASE IS CAUSED BY?

A

Neisserria meningitidis

68
Q

MENINGOCOCCAL DISEASE

A

can cause septicemia or meningitis or both

septicemia has higher mortality rate

69
Q

how many neisserria meningitdis serotypes are there?

A

3

A, B, C

70
Q

most common in Uk?

A

B

71
Q

commonest worldwide?

A

A

72
Q

which incidence tripled in 5 years prior to Men-C vaccine?

A

C

73
Q

where is the bacteria found in 25% adults?

A

•NORMAL NASOPHARYNX FLORA

74
Q

how is infection spread?

A

INFECTED RESPIRATORY SECRETIONS

75
Q

what is the route of infection?

A

•INHALATION ⇢ NASOPHARYNX ⇢ BLOOD STREAM ⇢ INVADE BBB CELLS ⇢ MENINGEAL SPACE

76
Q

when does infection occur?

A

SHORTLY AFTER COLONISATION

PROBABLY BEFORE IMMUNE RESPONSE HAS DEVELOPED

77
Q

what is the treatment?

A

•BENZYLPENICILLIN OR CEFOTAXIME

78
Q

how to identify bacteria?

A

Gram negative diplococci

79
Q

what media will grow well on?

A

enriched media in 5% CO2

Eg chocolate agar

80
Q

what other identifying characteristics?

A
  • Oxidase positive
  • Ferment glucose and maltose
  • DNA’ase negative
81
Q

how can antibodies be used in identification?

A

•Slide agglutination with antibodies directed against meningococcal polysaccharides

82
Q

how can pcr be used in identification?

A

identifying ctrA and siaD gene

83
Q

the ctrA gene?

A
  • Export of polysaccharide capsule
  • Common to all meningococci
84
Q

when used pcr screening be used to be find ctrA gene?

A

invasive N. meningitidis disease

85
Q

the siaD gene?

A

Capsular synthesis

  • Serogrouping assay
  • Epidemiological value

medical microbiology (29 decks)

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