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Respiratory > Lecture 19- Tuberculosis > Flashcards

Lecture 19- Tuberculosis Flashcards

1
Q

What is TB caused by?

A

Mycobacterium tuberculosis

  • Aerobic
  • Acid and alcohol fast bacilli
  • Slow growing
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2
Q

Demographics and risk factors

A
  • Non-UK born/recent migraines
    • South Asia 54%
    • Sub-Saharan Africa 29%
  • HIV
  • Immunosuppressed
  • Homeless
  • Drug users, prison
  • Close contacts
  • Young adults (also higher incidence in elderly)
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3
Q

How can we stain for tuberculosis?

A

Sputum smear stained with Ziehl-Nielsen method

Takes 2-6 weeks to grow colonies

–> cant tell if TB alive or dead

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4
Q

in the UK TB is mainly found in

A

non-UK born

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5
Q

How does TB transmit from person to person?

A
  • infected droplets from coughing and sneezing
  • Infectious dose 1-10 bacilli
  • Contagious, but not easy to acquire infection
  • Need prolonged exposure to facilitate transmission (at least 8-hours /day up to 6 months)
    • Households
    • Prisons
    • School
  • Lots of factors need to be fulfilled for transmission
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6
Q

Where is the most common site of pulmonary TB?

A

Right lung apex as high pO2 in these areas compared to the rest of the lungs

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7
Q

pathogenesis of TB

A
  • Alveolar macrophages phagocytose MTB but cannot kill them as cell wall lipids of MTB block fusion of phagosome and lysosome
  • Macrophages initiate cell mediated immunity so activated macrophages can come and kill MTB, takes about 6 weeks
  • Granulomatous reaction from macrophages
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8
Q

primary complex (Ghons focus and draining lymph node) can have 3 outcomes

A
  1. Active primary disease (5%)
  2. Initial containment of infections
    • Heals/self cure
    • Post primary infection TB
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9
Q

What could cause a latent TB infection to reactivate?

A
  • HIV
  • Chemotherapy
  • Malnutrition
  • Old age
  • corticosteroids
  • immunosuppressive therapy e.g. organ transplant
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10
Q

What is the likelihood of someone being infected with TB actually developing the active disease?

A

10% lifetime risk

  • 5% develop primary TB at initial infection when primary complex does not heal
  • 5% develop post primary TB up to 60 years after initial infection
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11
Q

TB with symptoms=

A

infectious

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12
Q

Primary TB become symptomatic after first exposure to TB

A
  • Ghon focus/complex
  • Limited by CMI
  • Usually asymptomatic
  • Rare allergic reactions include erythema nodosum
  • Occasionally symptomatic and can also disseminate
  • i.e. military and extra pulmonary
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13
Q

The general symptoms of TB disease include

A

Unexplained weight loss

Loss of appetite

Night sweats

Fever

Fatigue

Chills

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14
Q

The symptoms of TB of the lungs include

A

Coughing for 3 weeks or longer

Hemoptysis (coughing up blood)

Chest pain

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15
Q

Post-primary TB

A
  • reactivation by exogenous re-infection
    • latent –> disease
  • much more symptomatic
  • >5 years after primary infection
  • 5-10% risk per lifetime
  • Clinical presentation
    • Pulmonary or extra-pulmonary
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16
Q
A
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17
Q

how can we test for latent infection

A

IGRA (QuantiFERON)

Tuberculin skin test

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18
Q

IGRA (QuantiFERON)

A

MTB antigens can make the body produce interferon gamma. Lymphocytes from the patient are cultured with MTB antigens and if T lymphocytes have been exposed before they will produce interferon gamma. The MTB antigen is not present in BCG or atypical mycobacteria so can distinguish latent from BCG vaccine

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19
Q

Tuberculin Skin Test:

A

Protein from MTB injected intradermally. Skin reaction 48-72 hours later indicates previous TB exposure, type IV hypersensitivity reaction to MTB

indicates sensitive T cells

20
Q

positives and negatives of tubercukin skin test

A

Positives

  • Cheap
  • Lab infrastructure not required
  • Evidence to support ability to predict active disease in those that are latently infected

Negatives

  • False positives- BCG non TB
  • False negatives (immunocompromised i.e. HIV/drugs/ advanced disease)
21
Q
A
22
Q

positives and ngeatives of IGRA

A

Advantages

  • Antigens are only found in M. tb (not in BCG)

Disadvantages

  • Cannot distinguish latent and active TB
  • Similar problems with sensitivity and specificity
23
Q

What are some of the changes a patient may have with post primary TB?

A
  • Cavity formation: liquefaction of caseous material. Fibrous tissue usually around periphery of lesions
  • Haemorraghe: extension of caseous process into vessels. leads to haemoptysis
  • Spread to rest of lung
  • Pleural effusion: seeding of TB into pleura or hypersensitivity
  • Miliary TB: rupture of caseous pulomnary focus into blood vessel so widespread dissemination through body
24
Q

What are some sites of extrapulmonary TB?

A

Miliary TB

  • Bacteria spreading through the blood stream –> widespread infection
  • Lymph nodes
  • Bones
  • Joints
  • CNS
  • GI tract
  • Urinary tract
  • brain (tb meningitis)
25
Q

when does milliary tb occur

A
  • Either during primary infection or during reactivation
  • Lungs are always involved- but few respiratory symptoms
    • Fever, very unwell, dry cough
  • Often multiple organs involved
  • Other organ involvement is variable
    • Headaches suggest meningeal involvement
    • Pericardial- pleural effusions small
    • Ascites may be present
    • Retinal involvement (Choroid tubercles seen)
26
Q

What are some clinical features of pulmonary TB?

A
  • Gradual onset over weeks or months
  • Tiredness
  • Malaise
  • Weight loss
  • Fever
  • Sweats
  • Cough with haemoptysis
  • Can be asymptomatic even when CXR abnormal
  • Crackles may be present
  • Signs of pleural effusion or fibrosis
27
Q

What does a CXR of TB look like?

A

Ghons focus

  • Patchy solid lesions
  • Cavity solid lesions
  • Streaky fibrosis
  • Flecks of calcification
28
Q

How do we diagnose active TB?

A
  • radiology most important
  • microscopy
  • culture
  • histology
29
Q

TB microscopy

A
  • Rapid and cheap test
  • Zeal-neelson (ZN)stain used (acid-fast)
    • Pink bacilli
      • For test to be positive = need at least 5000 bacilli
        • Smear positive case
    • Cannot differentiate MTB from NTM
    • Cannot differentiate live and dead organisms
30
Q

why doesnt the TB gram stain

A

encapsulated

31
Q

TB culture- second most important

*

A
  • Remains gold standard for TB diagnostics
  • One of the most sensitive methods for detecting mycobacteria
  • Solid and liquid culture system
  • Has improve automated culture technology
  • Allows identification and susceptibility testing
32
Q

types of TB culture

A

Lowenstein jensen slopes

Automated TB culture

Additional test

33
Q

Lowenstein jensen slopes

A
  • Bacilli takes a long time to grow in this (2-6 weeks)
    • Will need to be sent for microscopy identification
34
Q

Automated TB culture

A
  • Liquid culture medium
  • Sample goes into automated machine
  • Much more sensitive than solid cultures
  • Detect growth of TB bacilli by measuring the change in pH (CO2 conc)
  • Can detect growth much earlier (10-14 days)
35
Q

additional tests

A
  • Nucleic acid amplification test (NAAT)
    • Rapid diagnosis of smear positive
    • Drug resistance mutations
  • GWAS
36
Q

What does TB look like using histology?

A
  • Granuloma with central caseous necrosis (cheese) surround by epitheliod macrophages, langhans giant cells and lymphocytes
37
Q

How do we treat TB?

A
  • Rifampicin (red urine)
  • Isoniazid (INAH)
  • Pyrazinamide
  • Ethambutol

All 4 drugs for 2 months and then just R and INAH for a further 4 months. Give pyridoxine with INAH to stop peripheral nerve damage

low compliance

38
Q

multidrug therapy

A
39
Q

Why do we give 4 drugs for TB?

A

One drug would allow selection of resistant strains, less likely to be resistant to all three drugs

pts at risk- those not taking the medication

40
Q

What should you do if you diagnose a patient with TB?

A
  • Isolate and notify public health
  • PPE
  • Contact trace and vaccinate
41
Q

difference between latent and active disease

A
42
Q

adverse affect of drugs

A
43
Q

What are some extra-pulmonary signs of miliary TB?

A
  • Headaches as meningeal involvement
  • Pericardial and pleural effusions
  • Retinal involvement
  • Ascites
44
Q

Offer prophylactic drugs to pts with

A

latent TB – to kill dormant TB- reduce number of people with active disease

45
Q

BCG- Bacilli Calmette-Guerin vaccine

A
  • Live attenuated M.bovis strain
  • Given to babies in high prevalence communities
  • 70-80% effectiveness in preventing severe childhood TB
  • Protection wanes
  • Little evidence in adults
  • Not part of routine childhood vaccination schedule only given to neonates/ infants / older children thought to have an increased risk of coming into contact with TB
  • Other indication
    • New entrants from high-risk areas
    • Health workers
    • Close contacts of active resp TB
    • Other groups- ref green book
  • Always consider HIV testing where appropriate before giving BCG
46
Q

Ghon focus

A

ghon focus- granuloma with associated WBC

ghon comples- ghon focus with associated lymph node

47
Q

granuloma formation

A
  • Granuloma
    • A collection of epithelioid histiocytes (macrophages) with surrounding lymphocytes

May also see giant cells within granuloma

Respiratory (27 decks)

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