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Respiratory System > Tuberculosis > Flashcards

Tuberculosis Flashcards

1
Q

Which organism causes TB?

A

Myobacterium Tuberculosis

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2
Q

What are the characteristics of the organism that causes TB

A

Characteristics of Myobacterium Tuberculosis:

  • Obligate aerobe
  • Acid and alcohol fast bacilli (staining)
  • Non- motile rods
  • Long chain fatty acid and glycolipids in cell wall gives structural rigidity
  • Slow growing
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3
Q

What are some of the risk factors for getting TB?

A
  • Non-UK born / recent migrant from South Asia or Sub-Saharan Africa
  • HIV
  • Immunocompromised
  • Homeless
  • Drug user
  • Prisoner
  • Young adults
  • In close contact with someone who has TB
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4
Q

How is TB transmitted?

A

Spread by infected droplets

Droplet nuclei are small and suspended in air and can reach the lower airways

Contagious but need prolonged exposure of at least 8 hours/day for up to 6 months

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5
Q

Explain the pathogenesis of TB

A
  1. Inhaled aerosols of TB
  2. Engulfed by alveolar macrophages but unable to phagocytose
  3. Infected macrophages get into lymph nodes
  4. Initates develipment of cell mediated immunity
  5. Either progresses to active primary disease
  6. Or get a latent infection which will either self cure (95%) or reactivate (post primary TB)
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6
Q

How long does it take for activated macrophages that can kill MTB to develop?

A

6 weeks

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7
Q

What are some of the symptoms of TB?

A
  • Cough
  • Fever
  • Weight loss and anorexia
  • Night sweats
  • Haemoptysis
  • Breathlessness if pleural effusion
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8
Q

What is a Ghon focus/ complex?

A

Focus seen on CXR in someone with primary TB

Harm to lung is minimal, patient may be asymptomatic/ minimally symptomatic

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9
Q

What is post primary TB?

A
  • Reactivation or exogenous re-infection
  • Occurs >5 years after primary infection
  • 5-10% lifetime risk of development
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10
Q

What is the primary complex in primary TB infection?

A

Ghon’s focus + the draining lymph node (hilar node)

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11
Q

What are some of the risk factors for reactivation of TB?

A
  • HIV
  • Substance abuse
  • Prolonged therpay with steroids
  • TNF-alpha antagonists
  • Organ transplant
  • Haematological malignancy
  • Severe Kidney Disease
  • Diabetes Mellitus
  • Silicosis
  • Low Body Weight
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12
Q

What is extra-pulmonary TB? In which patients is this seen?

A

When TB spreads to other places than the lungs:

  • Larynx
  • Lymph Nodes
  • Pleura
  • Brain
  • Kidneys
  • Bones and Joints

Seen more often in: HIV infected/ immunocompromised people and children

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13
Q

What is Miliary TB?

A

When TB is carried to all parts of the body through the blood stream

RARE

Seen in very young children or very immunosuppressed patients

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14
Q

What do you see in histology of someone infected with TB?

A

Caseating Granulomta of Lagnhan giant cells

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15
Q

What signs would you find on examination of someone with TB?

A
  • Often no chest signs despite CXR abnormality
  • May have crackles in affected area
  • Signs of cavitation and fibrosis in extensive disease
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16
Q

How do you investigate pulmonary TB?

A
  • Chest X Ray
  • Sputum samples: 3 early morning samples of 5ml minimum volume
  • Induce sputum if not producing any, may need alveolar lavage
  • Bronchoscopy in patients with dry cough
17
Q

What are classic findings on pulmonary TB chest X ray?

A
  • Apex of lung often involved
  • Ill defined patchy consolidation
  • Cavitation
18
Q

What is the gold standard for TB diagnostics?

A

TB Culture although this can take a long time!

19
Q

What test would indicate that TB is infectious?

A

Smear postive case

Seeing TB bacilli under microscope in Zeihl-Neilson staining

20
Q

What is the fastest way to identify primary TB?

A

Nucleic Acid Amplification Test (PCR)

  • Gives rapid diagnosis of smear positive cases
  • Shows drug resistant mutations
21
Q

Explain the tuberculin skin test

A
  • Tuberculin injected intradermally and read 48-72 hours later
  • If antigen is present it will produce a hypersensitivity reaction
22
Q

What are the advantages/ disadvantages of the tuberculin skin test?

A

Advantages:

  • cheap
  • no lab evidence required

Disadvantages:

  • False positives
  • False negatives if immunocompromised
  • Subjective interpretation
23
Q

Which blood test can you use to check for latent TB that specifically looks for the antigen to mycobacterium TB ?

A

Inferon Gamma Assays

24
Q

Explain how the interferon gamma assay works

A
  • T cell based assay
  • Antigen presenting cells present antigens to primed T cells in vitro
  • Blood from patient cultured with the antigens to mycobacterium tuberculosis. If previous exposure to TB, T Lymphocytes produce interferon gamma response
25
Q

Which first line drugs are used in the treatment of TB?

A

Think RIPE

  • *R**ifampicin
  • *I**soniazid
  • *P**yrazinamide
  • *E**thambutal
26
Q

What second line treatments can be offered if 1st line cannot be taken?

A
  • Quinolones
  • Injectables
27
Q

Why are a combination of 4 antibiotics used as first line treatment?

A

Mycobacterium tuberculosis strain contains small number of naturally drug resistant organisms from spontaneous mutation

The likelihood of being resistant to all 4 drugs is unlikely and reduces that changes of resistant strains emerging

28
Q

How long does the patient need to be treated with anti-TB drugs for?

A
  • 3 or 4 drugs taken for 2 months
  • Followed by Rifampicin and Isoniazid for 4 months
  • Minimum 6 months treatment
29
Q

Why must Vitamin B6 (pyridoxine) be given alongside isoniazid for treatment of TB?

A

To prevent peripheral nerve damage

30
Q

How can adherance to TB therapy be monitored?

A
  • Directly observed therapy
  • Video observed therapy
31
Q

What things increase the likelihood of a drug resistance to anti-TB drugs?

A
  • Previous TB infection and prescription
  • HIV +
  • Known contact with multi-drug resistant TB
  • Failure to respond to conventional treatment
  • >4 months smear +ve
  • >5 months culture +ve
32
Q

What vaccine can be given to prevent TB?

Explain the strain and how it is used

A

BCG vaccine

A strain of live attenuated M. bovis strain

Given to babies in hiigh prevalence communities only

Respiratory System (20 decks)

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