Session 6

Question 1

List some properties of TB bacilli

Answer 1

Aerobic, acid and alcohol fast and grow slowly on culture

Question 2

How is TB transmitted?

Answer 2

Person to person by aerosolised droplets. Prolonged exposure facilitates transmission.

Question 3

How long should anti TB chemotherapy last?

Answer 3

6 months to eliminate disease. Infectivity of sputum if minimum after 2 weeks

Question 4

Describe the body’s response to Mycobacterium tuberculosis

Answer 4

Phagocytosed by alveolar macrophages but they are unable to kill them - cell wall prevents fusion with lysosomes. Activated macrophages are developed with enhanced ability to kill - this takes ~6 weeks.
This causes a spherical granuloma with central caseation, surrounded by epitheliod macrophages, Langerhans giant cells and lymphocytes

Question 5

What happens upon primary infection with TB?

Answer 5

Usually a development of a sub pleural primary/Ghons focus in any lung zone. Primary focus + draining lymph = primary complex. Leads to primary TB if it doesn’t heal

Question 6

Describe latent TB

Answer 6

Most primary infections heal but usually some TB bacilli spread via bloodstream to a different part of the lung or to a different organ before healing. It can then persist in the host without causing disease. 10% lifetime risk of developing active disease

Question 7

What causes clinical TB?

Answer 7

Reactivation of latent TB When the patients immune system fails (immunosuppression, HIV, old age, malnutrition) - most common
Reinfection

Question 8

How is latent TB detected?

Answer 8

Positive tuberculin skin test - hypersensitivity to proteins derived from mycobacteria

Question 9

How can the infection be disseminated to other lung zones?

Answer 9

Spread of caseous material through bronchial tree. Can lead to development of inflammatory exudate and hence tuberculosis pneumonia

Question 10

How is TB diagnosed?

Answer 10

Clinically-persistent cough (not always productive), haemoptysis, unresolved pneumonia, non-specific fever weight loss
Radiologically - CXR shows pulmonary shadowing which may be patchy/cavitated solid regions, streaky fibrosis or calcification
Identification of TB bacilli by smear and culture

Question 11

How is TB treated?

Answer 11

3/4 drugs for 2 months then Rifampicin and isoniazid for 4 months to combat resistance
Treatment has low adherence

Question 12

What is milary TB?

Answer 12

Spread to all parts of the body through bloodstream

Question 13

What are risk factors for the development of TB?

Answer 13

Recent migrants, HIV, homeless, drugs, other immunocompromise, malnutrition

Question 14

What is a BCG?

Answer 14

Live attenuated strain of M. Bovis most effective in childhood

Question 15

What is asthma?

Answer 15

Chronic inflammatory disorder of the airway with REVERSIBLE airway obstruction

Question 16

Describe the pathogenesis of asthma

Answer 16

Environmental trigger breathed in -> inflammation driven by TH2 cells -> type 1 hypersensitivity reaction -> airway narrowing -> remodelling

Question 17

List some possible allergens for asthma

Answer 17

Indoor - pets, house dust mite, mound/fungus
Outdoor - pollens, tobacco, pollutants
Others - cold, medications (NSAIDs/B-blockers)

Question 18

What are the effects of airways narrowing seen in practice?

Answer 18

Wheeze (expiratory), dry cough, breathlessness and chest tightness. Worse at night (increased vagal activity)
Obstructive pattern on spirometry (gold standard for diagnosis along with history) and flow volume loops which shows reversibility with bronchodilators
Increased residual volume

Question 19

What type of respiratory failure does asthma present with?

Answer 19

Mild to moderate attack - type 1

Severe attack - type 2 due to extensive involvement of airways and exhaustion

Question 20

What is the treatment for asthma?

Answer 20

Patient education (using inhalers/avoiding triggers)
Short acting B agonist (SABA-salbutamol). If >3 times a week or nocturnal symptoms, step up.
Steroid - reduces inflammation, preventor
LABA (longer acting) is steroids unsuccessful

Question 21

What are signs of severe/life threatening asthma?

Answer 21

Severe - No wheeze, tachycardia, high RR, cannot complete sentences
Life threatening - central cyanosis, altered consciousness, bradycardia, exhaustion

Question 22

What are treatments for life threatening asthma?

Answer 22

O2, salbutamol nebulisers, IV access, ITU admission

Question 23

What are the changes in the airways seen in asthma?

Answer 23

Hyper responsiveness and constriction of smooth muscle
Thick Mucus hypersecretion
Mucosal oedema
Inflammatory cell infiltrate
Epithelial damage due to chemical mediators -> remodelling (SMC hypertrophy)

Question 24

Why do some asthmatics experience difficulty breathing in?

Answer 24

They have increased residual volume so the lungs are starting from a less compliant more stretched position