Hypersensitivity pneumonitis

Question 1

What is hypersensitivty pneumonitis definition?

Answer 1

Hypersensitivity pneumonitis (HP), is the result of non-IgE mediated immunological inflammation of the lungs.

Question 2

Epidemiology of HP

Answer 2

Usually a disease of adults

Question 3

What is HP usually caused by?

Answer 3

Hypersensitivity pneumonitis can be caused by a variety of organic antigens e.g. coffee bean dust, moldy sugarcane, bacterial spores. The resulting disease is often named for the profession at risk.

Question 4

What are the different types of lungs?

Answer 4

• Bird-fanciers lungis a reaction to bird droppings
• Farmers lungis a reaction to mouldy spores in hay
• Mushroom workers’ lungis a reaction to specific mushroom antigens
• Malt workers lungis a reaction to mould on barley
• Humidifier or air conditioner lung: caused by inhaling the spores of actinomycetes that grow in the warm water reservoirs

Question 5

RFs of HP

Answer 5

• Pre-existing lung disease
• Specific occupations e.g. farmers, cattle workers, ventilation system workers, vets and those jobs that involve working with chemicals
• Bird keeping
• Regular use of hot tubs

Question 6

What is HP?

Answer 6

when a person’s immune system reacts excessively to something that’s inhaled, causing lung inflammation.

The antigens are breathed in and settle in the alveolus. It is picked up by an alveolar macrophage which takes it to the nearest lymph node.

Question 7

What happens in the lymph node?

Answer 7

Alveolar macrophage attracts CD4 T-helper cells which release cytokines to attract more immune cells.
Leads to Type III and Type IV hypersensitivty reactions

Question 8

What happens in a type 3 hypersensitivity reactio

Answer 8

• develops over a period of a few hours
• activated b cells release IgG ABs that bind to the antigen
• forms clusters of antigen antibody deposits
• deposits activate the complement system
• inflammation and necrosis of nearby capillaries

Question 9

What happens in a type IV hypersensitivty reaction

Answer 9

develops over 2-3 days

• large numbers of activated macrophages and T-cells come to the site of antigen exposure and surround it
• forming a granuloma.
• If the antigen isn’t removed, then the immune system can cause lasting damage to the alveoli.

Question 10

What does chronic inflammation lead to?

Answer 10

• damage to elastin fibres
• results in fibroblasts entering tissue to deposit more fibrin
• excess fibrin and less elastin = restrictive lung disease
• scarring results in loss of alveolar function

Question 11

Acute clinical manifestations of HP

Answer 11

• Fever
• Rigors
• Headache
• Myalgia
• Shortness of breath
• Cough
• Chest tightness

Question 12

Chronic clinical manifestations of HP

Answer 12

More gradual onset

• Sustained shortness of breath
• Cyanosis and clubbing may develop
• Respiratory failure

Question 13

Investigations for HP

Answer 13

• Chest x-ray: shows diffuse infiltrate
• Lung function tests: abnormal
• ESR: raised
• Bronchoalveolar lavage: high number of lymphocytes and mast cells
• Lung biopsy: small granulomas around the bronchioles, and lymphocyte infiltration in the alveolar walls
• Identify trigger: can use inhalation challenge - expose patient to potential triggers and monitor symptoms

Question 14

Management of HP

Answer 14

• Eliminate trigger
• Steroids: can be used to help with symptoms
• Give oxygen, where necessary