Extrinsic Allergic Alveolitis

Question 1

What is EAA?

Answer 1

Hypersensitivity pneumonitis (HP), also known as extrinsic allergic alveolitis, is the result of non-IgE mediated immunological inflammation. HP is caused by repeated inhalation of non-human protein, which can be of natural plant or animal origin or can be the result of a chemical conjugated to a human airway protein, such as albumin.

Question 2

What are the risk factors to EAA?

Answer 2

Smoking
Viral infection
Exposure to avian protein, mould, bacterial and acid anhydride antigen
Exposure to diisocyanates, metal-working fluid
Nitrofurantoin, methotrexate, roxithromycin, rituximab
Herbal supplements with ayurvedic medicine

Question 3

What is the epidemiology of EAA?

Answer 3

The prevalence of HP is not precisely known. It most probably varies with the antigen, the exposure concentration, and as yet unidentified host factors.

Question 4

What are the signs and symptoms of EAA?

Answer 4

Exposure in history
Dyspnoea
Non productive cough
Productive cough
Malaise
Fever
Weight loss
Bibasilar or diffuse rales
Clubbing

Question 5

What investigations are needed for EAA?

Answer 5

Immunological response to causative agent

Bloods
FBC
Leukocytosis
Normochromic, normocytic anaemia

ESR
Elevated

Albumin
Low

CXR
Infiltrates, nodular or patchy
Fibrosis

CT chest
Ground glass shadowing
Poorly defined micronodules
Mosaic attenuation
Centrilobular nodules
Relative basal sparing

Pulmonary function test
Restrictive
Mixed restrictive/ obstructive

Diffusing lung capacity of Carbon monoxide
Decreased

Bronchoalveolar lavage
Positive antibody and lymphocytosis

Lung biopsy
Bronchocentric infiltrates incl. Lymphocytes, plasma cells, neutrophils, foamy macrophages and non-caseating granulomas
Interstitial fibrosis