Pathology of Pulmonary infections

Question 1

Pneumonia

Answer 1

Infection involving the distal airspaces usually with inflammatory exudation.
Fluid filled spaces lead to consolidation.

Question 2

How do you classify pneumonia?

Answer 2

By clinical setting (eg: community acquired pneumonia)
By organism (pneumococcal etc.)
By morphology (lobar pneumonia, bronchopneumonia)

Question 3

What organisms are involved with pneumonia?

Answer 3

Viruses - influenza, measles
Bacteria
Chlamydia, mycoplasma
Fungi

Question 4

What is lobar pneumonia?

Answer 4

Confluent consolidation involving a complete lung lobe.
Most often due to streptococcus pneumoniae.
Can be seen with other organisms.

Question 5

Where is lobar pneumonia usually found??

Answer 5

Usually community acquired.

Classically in otherwise healthy young adults.

Question 6

What is the classical acute inflammatory response?

Answer 6

Exudation of fibrin-rich fluid
Neutrophil infiltration
Macrophage infiltration
Resolution

Question 7

Complications of pneumonia?

Answer 7

Organisation (fibrous scarring)
Abscess
Bronchiectasis
Empyema

Question 8

What is bronchopneumonia?

Answer 8

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

Question 9

Where is bronchopenumonia usually seen?

Answer 9

Patients with:
COPD
Cardiac failure (elderly)
Complication of viral infection (influenza)
Aspiration of gastric contents

Question 10

What is a lung abscess?

Answer 10

Localised collection of pus
Tumour-like
Chronic malaise and fever
Context - aspiration

Question 11

What is bronchiectasis?

Answer 11

Abnormal fixed dilatation of the bronchi
Usually due to fibrous scarring following infection (pneumonia, TB, cystic fibrosis)
Also seen with chronic obstruction (tumour)
Dilated airways accumulate purulent secretions

Question 12

Tuberculosis

Answer 12

Mycobacterial infection
Chronic infection described in many body sites – lung, gut, kidneys, lymph nodes, skin….
Pathology characterised by delayed (type IV) hypersensitivity (granulomas with necrosis)

Question 13

Organisms involved with TB

Answer 13

M. tuberculosis/M.bovis main pathogens in man.
Others cause atypical infection especially in immunocompromised host. Pathogenicity due to ability;
to avoid phagocytosis
to stimulate a host T-cell response

Question 14

Immunity in TB

Answer 14

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

Question 15

Hypersensitivity (type IV) to TB

Answer 15

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

Question 16

How long does your first exposure to TB last??

Answer 16

Primary TB: 1st exposure and up to 5 years afterwards

Question 17

Secondary TB

Answer 17

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 18

Tissue changes in Primary TB

Answer 18

Small focus (Ghon focus) in periphery of mid zone of lung
Large hilar nodes (granulomatous)

Question 19

Tissue changes in Secondary TB

Answer 19

Fibrosing and cavitating apical lesion (cancer an important differential diagnosis

Question 20

Why does disease reactivate?

Answer 20

Decreased T-cell function (age, coincident disease (HIV), immunosuprressive therapy (chemo, steroids…)
Reinfection at a high dose or with more virulent organism