Pathology of Pulmonary Infections

Question 1

How can pneumonia be classified?

Answer 1

By clinical setting (e.g. community acquired pneumonia)
By organism (mycoplasma, pneumococcal etc)
By morphology (lobar pneumonia, bronchopneumonia)

Question 2

What is pneumonia?

Answer 2

Infection involving the distal airspaces usually with inflammatory exudation/localised oedema
Fluid filled spaces lead to consolidation

Question 3

Describe the 4 steps of pneumonia?

Answer 3

• Exudation of fibrin-rich fluid
• Neutrophil infiltration
• Macrophage infiltration
• Resolution

Question 4

What is lobar pneumonia?

Answer 4

Confluent consolidation involving a complete lung lobe which is most often due to Streptococcus pneumoniae (pneumococcus).
Can be seen with other organisms (Klebsiella, Legionella)

Question 5

What is Bronchopneumonia? Which organisms cause it?

Answer 5

Infection starting in airways and spreading to adjacent alveolar lung.
Most often seen in the context of pre-existing disease.

Strep. Pneumoniae, Haemophilus influenza, Staphylococcus, anaerobes, coliforms

Question 6

What is Bronchiectasis?

Answer 6

abnormal fixed dilatation of the bronchi, usually due to fibrous scarring following infection - complication of pneumonia

Question 7

What is Tuberculosis?

Answer 7

Mycobacterial infection. Chronic infection described in many body sites – lung, gut, kidneys, lymph nodes, skin

characterised by delayed type IV hypersensitivity (granulomatous)

Question 8

What are the main pathogens in TB?

Answer 8

M. tuberculosis

M.bovis

Question 9

Describe how immunity and hypersensitivity occur in TB?

Answer 9

Immunity = T-cell response to organism enhances macrophage ability to kill mycobacteria

Hypersensitivity = T-cell response causes granulomatous inflammation, tissue necrosis and scarring

Question 10

Describe the pathology of primary TB - first exposure?

Answer 10

inhaled organism phagocytosed and carried to hilar lymph nodes. 
Immune activation (few weeks) leads to a granulomatous response in nodes (and also in lung) usually with killing of organism.
 In a few cases infection is overwhelming and spreads

Question 11

Describe the pathology of secondary TB - second exposure?

Answer 11

reinfection or reactivation of disease in a person with some immunity, disease tends initially to remain localised, often in apices of lung.
Can progress to spread by airways and/or bloodstream

Question 12

How is TB diagnosed?

Answer 12

broncho-alveolar lavage

biopsy

Question 13

Why would TB reactivate?

Answer 13

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