Hypersensitivity Pneumonitis

Question 1

What is hypersensitivity pneumonitis?

Answer 1

A type 3 hypersensitivity reaction to an antigen. Also called extrinsic allergic alveolitis (EAA).

May be acute or chronic.

Question 2

What are common variants of hypersensitivity pneumonitis?

Answer 2

Farmer’s lung
Bird fancier’s lung
Malt worker’s lung

Question 3

How does acute EAA present?

Answer 3

The patient will have flu-like symptoms. May be accompanied by pyrexia, crackles (but no wheeze) or hypoxia.

Question 4

What investigations are necessary to diagnose an acute hypersensitivity pneumonitis?

Answer 4

CXR - will show widespread pulmonary infiltrates
History

Question 5

How is acute EAA treated?

Answer 5

Oxygen therapy
Steroid therapy
Avoid causative agent

If severe fibrosis, anti-fibrotics may be needed.

Question 6

What is the pathology in chronic EAA?

Answer 6

The patient has had repeated exposure over a number of years, thus will describe progressive breathlessness and cough, with examination finding crackles.

Question 7

How does a restrictive defect show on spirometry?

Answer 7

Will have low FEV1 and low FVC, resulting in no/mild reduction in ratio.

Question 8

What antibodies are implicated in type 3 hypersensitivity?

Answer 8

IgG.

Question 9

How will chronic EAA appear on a CXR?

Answer 9

Will have pulmonary fibrosis within the upper zones.

Question 10

Alongside CXR, what other tests may be used to diagnose chronic hypersensitivity pneumonitis?

Answer 10

CT scan (will show ‘ground glass’ opacities)
Bloods (will have antibodies present against causative agent)
Lung biopsy (if still unclear)