Tuberculosis (Respiratory)

Question 1

What findings would someone with TB have on bronchoscopy?

Answer 1

Tubercles and pus.

Question 2

How long does it take to cure TB?

Answer 2

6 months.

Question 3

Where is there quite a lot of TB?

Answer 3

Eastern Europe, Africa and Asia.

Question 4

Describe the development of TB after infection with mycobacterium tuberculosis.

Answer 4

TB enters airway and then alveoli. Forms granulomas in the alveolus which contain the bacterium. If the bacteria break out of this granuloma then disease occurs.

Question 5

When people are infected with TB, what are the percentage chances that they will remain well or develop the disease?

Answer 5

90% remain well, 5% get primary TB and 5% get reactivation of latent disease.

Question 6

What are the symptoms and signs of TB?

Answer 6

General: weight loss, malaise, night sweats. Respiratory symptoms and signs: cough, haemoptysis, breathlessness, upper zone crackles. Meningeal: headache, drowsy, fits. GI: pain, bowel obstruction, perforation, peritonitis. Spinal: pain, deformity, paraplegia. Lymphadenopathy. Cold abscess. Pericardial: causes cardiac tamponade. Renal: renal failure. Septic arthritis: cold monoarthritis of large joints. Adrenal: hypoadrenalism.

Question 7

How long does ZN staining take?

Answer 7

A lot of time.

Question 8

If someone is smear negative but culture positive, are they regarded as infectious?

Answer 8

No as the number of mycobacterium in their sputum is tiny.

Question 9

What is the most to least sensitive tests for TB?

Answer 9

Culture (picks up other mycobacteria, gives full range of sensitivities) -> PCR -> ZN stain.

Question 10

What antibiotic is TB resistant to?

Answer 10

Rifampicin.

Question 11

What is the histology of TB?

Answer 11

Multinucleate giant cell granulomas, caseating necrosis, sometimes visible mycobacteria.

Question 12

On CXR, what are the key characteristics of TB?

Answer 12

Upper lobe predominance, cavity formation, tissue destruction, scarring and shrinkage, heals with calcification.

Question 13

What is miliary TB?

Answer 13

When it gets in the bloodstream and goes everywhere in the chest. Looks like metastatic renal cancer.

Question 14

What is the therapy for TB? (important)

Answer 14

2 months of rifampicin, isoniazid, purazinamide, ethambutol. 4 months of rifampicin, isoniazid.

Question 15

What can aid adherence of TB tablets?

Answer 15

Combination pills.

Question 16

What are the side effects of rifampicin?

Answer 16

Colours urine and all bodily fluids orange. It is also a potent inducer of cytochrome enzymes which cause rapid breakdown of all steroid molecules including hormonal contraception and similar breakdown of opiate analgesics and many other drugs.

Question 17

What is a side effect of ethambutol?

Answer 17

Can cause optic neuritis (inflammation of optic nerve).

Question 18

How do you know if someone can move down from 4 drugs to 2?

Answer 18

There spit should be a negative test (may be some nonreplicating bacteria but not many replicating).

Question 19

What types of drug resistant TB are there and what are they resistant to?

Answer 19

Single agent (commonly isoniazid), multi-drug resistant (MDR, rifampicin and isoniazid), extended drug resistant (XDR, MDR and quinolone and injectable).

Question 20

What is the criteria for latent TB?

Answer 20

No evidence of active TB e.g. symptoms, x-ray, culture. Evidence of previous TB infection e.g. history of TB prior to 1960, calcification on x-ray, exposure to high prevalence area.

Question 21

What tests are there for latent TB?

Answer 21

Interferon gamma release assay (blood test) (IGRA), detects previous exposure to TB. Mantoux (tuberculin) test (skin test) - detects previous exposure to TB and BCG.

Question 22

What are the downsides to the tuberculin skin test (Mantoux)?

Answer 22

2 visits, intradermal injection, false positive if BCG vaccination given, cannot distinguish latent TB, cured TB, active TB or BCG.

Question 23

Describe the IGRA test.

Answer 23

Good for mass contact tracing but very expensive, looks for interferon gamma specific to antigens found only in m.tuberculosis.

Question 24

If someone has latent TB and you want to give them anti-TNF drugs what else would you give them?

Answer 24

6 months of isoniazid or 3 months of rifampicin and isoniazid.

Question 25

What diseases would you give anti-TNF therapy for and what dangers does this have?

Answer 25

Rheumatoid arthritis, Chrohn’s, psoriasis, ankylosing spondylitis. It can reactivate latent TB.

Question 26

What can be done to prevent TB?

Answer 26

Contact tracing to identify further cases, screening of high risk subgroups (esp migrants and prior to immunosuppressive agents), isolation of infectious cases, BCG immunisation.

Question 27

What is the BCG immunisation and when is it most effective?

Answer 27

Attenuated strain of mycobacterium bovis, intradermal injection, most effective in neonates of high risk familites.

Question 28

What disease is commonly associated with TB?

Answer 28

HIV.

Question 29

What tests will be able to detect what stage of TB?

Answer 29

Smear positive - active disease. Culture positive - subclinical disease. TST and IGRA - latent or active.

Question 30

What is the type of hypersensitivity reaction involved in TB?

Answer 30

Type IV - granulomatous inflammation, tissue necrosis and scarring.

Question 31

What are the tissue changes in primary TB?

Answer 31

Small focus (Ghon focus) in periphery of mid zone of lung, large hilar nodes (granulomatous).

Question 32

What are the tissue changes in secondary TB?

Answer 32

Fibrosing and cavitating apical lesion (cancer an important differential diagnosis).

Question 33

When does miliary TB occur?

Answer 33

Due to blood spread to lower lobe.

Question 34

Why does latent TB reactivate?

Answer 34

Decreased T-cell function with age, coincident disease (HIV), immunosuppressive therapy (steroids, cancer, chemotherapy). Also reinfection at high dose or with a more virulent organism.