Pneumonia and Tuberculosis

Question 1

Factors which predispose to a lung infection

Answer 1

Factors which predispose to a lung infection include

• loss or suppression of the cough reflex (immobility, unconsciousness, neuromuscular disorders etc) leading to aspiration.
• ciliary defects (e.g. smokers, squamous metaplasia, immotile cilia syndromes)
• accumulation of secretions (eg. cystic fibrosis, chronic bronchitis)
• immune deficiency local (alveolar macrophage inhibition) or systemic (IgA deficiency, HIV/AIDS).

Remember asplenic patients are particularly at risk of infection with encapsulated bacteria such as S. pneumoniae.

Question 2

Acute bronchitis

Answer 2

Inflammation of the large airways. Usually viral (RSV) can get superimposed bacterial infection (H. influenzae, S. pneumoniae). Characterised by cough, dyspnoea, tachypnoea and increased sputum production. Tests may reveal elevated white cell count (sensitive but non-specific) and there are rarely x-ray changes.

Question 3

Bronchiolitis

Answer 3

Inflammation of the smaller airways. Almost always in infants and almost always viral (RSV, parainfluenza). Can lead to a severe bronchopneumonia. Again, WCC is usually elevated and there may be changed in xray.

Question 4

Pneumonia

Answer 4

Alveolar inflammation with exudation of fluid into the alveoli and interstitium, leading to consolidation.

Question 5

Classification of pneumonias

Answer 5

1. Community acquired (including community acquired atypical pneumonia)
2. Health care associated (hospital acquired or nosocomial pneumonia)
3. Aspiration pneumonia
4. Pneumonia in immunocompromised

Question 6

Community acquired pneumonia

Answer 6

90% are Streptococcus Pneumoniae, remainder are mostly gram negative organisms (including Haemophilus influenzae).

Question 7

Aspiration pneumonia

Answer 7

Gastric contents aspirated, often associated with an impaired conscious state (including intoxication, anaesthesia, stroke, seizure), during vomiting or those with a poor gag reflex (stroke) - always protect your patients airways.

Question 8

Pneumonia in immunocompromised

Answer 8

Usually bacterial, may also be viral, fungal or other.

Question 9

Pneumonia patterns

Answer 9

1. Bronchopneumonia

2. Lobar pneumonia

Question 10

Bronchopneumonia

Answer 10

Diffuse, patchy consolidation, usually centred on bronchi or bronchioles, may affect more than one lobe (tends to occur in the very young and old).

Question 11

Lobar pneumonia

Answer 11

Affects most or all of a lobe, tends to occur in adults.

Question 12

What are the most important factors in determining the prognosis of pneumonia?

Answer 12

1. The extent of the disease
2. The causative agent
3. The co-morbidities of the patient

Question 13

Phases of lobar pneumonia

Answer 13

1. Congestion: occurs within the first 24 hours, outpouring of protein rich fluid into the intra-alveolar fluid associated with the presence of a few neutrophils and venous congestion.
2. Red hepatisation: last a few days, massive accumulation of neutrophils, fibrin, and extravasated red cells within the alveoli. Red, firm and airless - the lung appears like liver.
3. Grey hepatisation: accumulation of fibrin with destruction of red and white cells, leading to grey, solid lung.
4. Resolution: 8-10 days after onset, resorption of exudates and debris by macrophages or coughed up and restoration of the underlying lung architecture.

Question 14

Microscopic features of pneumonia

Answer 14

Neutrophils (early) and lymphocytes/macrophages (later) found.

Question 15

Clinical presentation of pneumonia

Answer 15

Patient present unwell, with fever, productive cough with purulent sputum. Modified by the administration of abx.

Question 16

Pneumonia complications

Answer 16

1. Pulmonary abscess
2. Emphysema
3. Organisation of the exudate leading to scarring
4. Bacterial dissemination to other organs and joints

Question 17

Pulmonary abscess

Answer 17

Complication of severe pneumonia due to pyogenic organisms (e.g. Staph. aureus) can result in a florid inflammatory response that leads to the formation of an abscess cavity filled with dead bacteria and inflammatory cells. Abscesses heal by repair (scar) rather than resolution and may persist despite antibiotics due to the poor penetration of antibiotics into the cavity.

Question 18

Empyema

Answer 18

Spread of infection to the pleural cavity causing an inflammatory fibrosuppurative reaction (ie pus in the pleural cavity and organisms may be seen on gram stain). May see a deterioration in patient recovery, spiking fevers, despite appropriate abc therapy. Drainage may be required

Question 19

Infective agent in tuberculosis

Answer 19

Tubercle bacilli (Mycobacterium tuberculosis) however lung diseases can also occur with other ‘atypical’ mycobacterium.

Question 20

Stages of tuberculosis

Answer 20

Tuberculosis has two main stages:

1. Primary TB
2. Post-primary TB (many different terms used)

Question 21

Primary tuberculosis

Answer 21

Most people may be asymptomatic, develop a fever and/or pleural effusion. The patient breathes in droplets containing tubercle bacilli and the bacillus enters the alveolar macrophages, replicating within the macrophages phagosomes.

In about 3-4 weeks a Th1 type immune response occurs, stimulated by APC expressing MHC-II associated mycobacterial antigens in the draining lymph node. Mature Th1 cells secrete IFN-gamma which drives the macrophages to kill the mycobacteria and the formation of granulomas ad caseous necrosis. Mantoux test becomes positive. The activated macrophages also secrete TND which recruits further monocytes from the blood, these monocytes differentiate into epitheloid histocytes present in the granulomatous response.

In most cases infection of a healthy individual is subclinical - indicated only by a tuberculin hypersensitivity reaction in a previously negative individual. Occasionally some patients do not contain the infe ction and they may go on immediately to post-primary TB. Lymphohaematogenous dissemination may result in the development of tuberculous meningitis.

Question 22

Ghon focus

Answer 22

Primary tuberculosis lesion - 10mm round lesion with a central zone of caseous necrosis surrounded by palisaded epitheloid histocytes, giant cells and lymphocytes. This is a caseating granuloma and is usually found in the mid zone of the lung. Usually this lesion will organise leaving a fibrocalcific nodule.

Usually the nodule contains living bacilli that may persist and cause post-primary TB.

Question 23

Ghon complex

Answer 23

Ghon focus with involvement of the hilar lymph nodes.

Question 24

Post-primary TB

Answer 24

May occur soon after primary infection or when the latent infection has been reactivated (tends to occur when the patient is relatively immunocompromised). Pulmonary TB is the most frequent form of post-primary disease. This tends to be clasically located in the apex of the upper lobes, maybe secondary to the high oxygen tension. A florid inflammatory response occurs, leading to a larger (1-2cm), cavitating lesion with a central area of caseous necrosis. The patient may be asymptomatic or have systemic symptoms including malaise, anorexia, weight loss, fever, night sweats and haemoptysis. The patient may be coughing up sputum that contains bacilli (therefore the patient needs to be isolated).

Ongoing and greater lung involvement may occur if the infection is not contained. May spread lymphohaematogenously throughout the lung and other parts of the body.

Question 25

Miliary TB

Answer 25

The spread of blood borne TB. Multiple small granulomas (about the size of millet seeds) are seen in the lungs and potentially other organs.

Question 26

Diagnosis of TB

Answer 26

Relies on recognition of acid-fast bacilli on microscopy or recognition of the patterns of cavitation and caseous necrosis either radiologically, biopsy or at autopsy.

Mantoux or tuberculin test, in which a small quantity of tuberculin protein is injected subcutaneously. An individual who has previously been exposed to TB will generate a stronger response than a non-exposed individual.

Question 27

Tuberculosis vaccine

Answer 27

BCG vaccine. Uses live attenuated strain of Mycobacterium bovix. It is a safe vaccine however confers limited protection (estimates of 20-60%) depending on the age of vaccination (much better in infants), the geographical ocation and the time since vaccination.