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Resp > Lecture 18 - TB > Flashcards

Lecture 18 - TB Flashcards

1
Q

TB demographics

A

Migrants from South Asia
HIV
Homeless
Drug users

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2
Q

Causative pathogen

A

Mycobacterium tuberculosis
M Bovis - cattle
M Africanum

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3
Q

M tuberculosis

A

Rod shaped

Obligate aerobe - normally in right apex as receives most O2

Long chain fatty acids, glycolipids and wax in cell wall so cant be stained

Slow growing

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4
Q

Stain

A

Acid alcohol fast stain

Red on Ziegler’s Neelson stain

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5
Q

Transmission

A

Respiratory droplets
Coughing
Sneezing

  • small dose (1-10 bacilli)- contagious but not easy to acquire
  • remain in air for long time
  • Prolonged exposure for atleast 8 hours/day for 6 months
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6
Q

Pathogenesis

A
  1. Inhales aerosol
  2. Engulfed by macrophages and phagocytosed.
  3. MTB is deposited in alveoli as unable to kill
  4. Spread to local lymph nodes
  5. Primary complex formed in Ghon’s focus and the primary lymph nodes are drained into the hilar lymph nodes
  6. Can progress to active disease where the primary complex does not heal (5%)
  7. Or there is initial containment of the infection
  8. Latent infection can occur where TB persists within host without causing disease for years
  9. Reactivation - post primary TB (5%) or heals 95%
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7
Q

Primary complex -

A

MTB in a phagosome is not killed initiates cell mediated immunity.

Activated macrophages try and kill MTB but exceeds capacity therefore granuloma formation (6 weeks)

Granuloma reaction - Ghon focus

  • spherical granuloma with central casseation - cheese like core necrosis
  • surrounded by Langerhan giant cells
  • casseation of lymph nodes + ghon focus = ghon complex

Fibrosis and calcification

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8
Q

Why is MTB not phagocytosed

A

Due to cell wall lipids blocking phagolysosome formation

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9
Q

Primary progression to active disease

A

TB bacilli in alveoli cause damage and spread

Generally asymptomatic with minimal damage

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10
Q

Post primary TB

A

Occurs when:

  • immunosuppressed
  • malnourished
  • Old
  • HIV
  • Drugs

Symptomatic

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11
Q

Latent infection

A

Before healing via lymph drainage to venous system, some bacilli enter the blood stream

Seeding in other parts of the lung and extra pulmonary sites

When immunocompromised, MTB can spread to the upper lobes (more oxygenated)

Memory T cells release cytokines and more caseous necrosis occurs, causing cavitation

TB can disseminate

  • via bronchial arteries and lymph channels to other parts of lung - can cause bronchopneumonia
  • via vascular system - military TB
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12
Q

Clinical TB infection

A

Symptomatic

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13
Q

Subclinical TB infection

A

Asymptomatic

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14
Q

Latent TB presentation

A 
Inactive 
TST and IFN +ve
CXR - normal
Sputum smear - -ve 
No symptoms 
Not infectious 
Not a case of TB
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15
Q

TB presentation

A 
Active - multiplying 
TST or blood test - +ve
CXR - cavity formation in shadowing
Sputum - +ve
Symptoms
Infectious 
A case of TB
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16
Q

Symptoms of TB

A 
Cough 
Fever
Weight loss
Night sweats
Malaise

Haemoptsis occasionally
Breathless with pleural effusion

17
Q

Miliary TB

A

Carried to all parts of the body through the blood stream

Multiple organs involved

  • Kidneys - sterile pyuria - WBCs in urine
  • brain meninges - meningitis
  • lumbar vertebrae - Pott disease
  • adrenal glands - Addison’s disease
  • liver - hepatitis

Diffuse specks on CXR

Rare

18
Q

Lung sounds

A

Maybe crackles

19
Q

Effects of TB

A

Can cause pleural effusion if pleura is affected

Lung fibrosis and cavitation if extensive

20
Q

Investigations

A

CXR - if positive IGRA or TST

Sputum - 3 early morning samples
Induced sputum

Microscopy

Bronchoscopy - patients with dry cough

NAAT

21
Q

CXR

A

Often right apex with patchy consolidation

Cavitation in consolidation

Healing causes fibrosis

22
Q

Sputum culture

A

Gold standard
Tuburcle bacillus
Rapid and cheap

Cannot differentiat MTB with non TB mycobacterium

23
Q

NAAT

A

Nucleic acid amplification tests

  • rapid diagnosis
  • drug resistant mutations
24
Q

Tuberculin sensitivity test (Montoux test)

A

TST

Protein derived from MTB (tuberculin) is injected intradermally

2-3 days later if there is presense of a skin reaction at the site, indicated previous exposure to TB or latent TB

25
Q

False positives

A

People with BCG vaccine

NMTB

26
Q

False negatives

A

HIV

Immunocompromised

27
Q

Interferon gamma assays

A

Specific MTB antigens stimulate the host production of interferon gamma

Lymphocytes are cultured from blood with the antigen

If exposed to TB before, T lymphocytes produce interferon gamma and identified

Unlikely to be positive due to BCG vaccine

28
Q

IFGA false positives

A

Less false positives as the MTB antigen is not found in the BCG vaccine or NMTB

29
Q

First line medication for TB

A

Rifampicin
Isoniazid
Pyrazinamide
Ethambutol

3 - 4 drugs for 2 months then Rifampicin and isoniazid for 4 months

30
Q

Contact tracing

A

Detect outbreaks

Notify public health

31
Q

Controlling TB

A

Detect and treat cases early
PPE
Negative pressure isolation
Vaccinations and address risk factors

32
Q

BCG vaccine

A

Live attenuated M. Bovis given to babies in high prevalence communities

33
Q

Primary TB

A

MTB is in phagosome but not destroyed
Multiplies within phagosome
Signs of infection - mild flu after exposure
Most asymptomatic

34
Q

Ghon focus

A

Central casseating necrosis surrounded by giant cells of Langerhan

35
Q

Ghon complex

A

Ghon focus + lymph nodes surrounded by casseating necrosis
Subpleural
Occur in lower lobes of lungs

36
Q

Ranke complex

A

Fibrosis and calcification of Ghon complex

Resp (22 decks)

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