Extrinsic allergic alveolitis

Question 1

What is extrinsic allergic alveolitis?

Answer 1

interstitial inflammatory disease of the distal gas-exchanging parts of the lung caused by inhalation of organic/antigenic dusts.

Question 2

What is extrinsic allergic alveolitis also known as?

Answer 2

hypersensitivity pneumonitis (HP).

Question 3

What is the aetiology of extrinsic allergic alveolitis?

Answer 3

In sensitised individuals, repetitive inhalation of allergens provokes a hypersensitivity reaction which varies in intensity + clinical course depending on the antigen.
In the acute phase, the alveoli are infiltrated with acute inflammatory cells.
Antigenic dusts include microbes + animal proteins

Question 4

Give examples of extrinsic allergic alveolitis

Answer 4

Farmer’s Lung: mouldy hay containing thermophilic actinomycetes
Pigeon Fancier’s Lung: blood on bird feathers + excreta
Maltworker’s Lung: barley or maltlings containing Aspergillus clavatus
Bagassosis or sugar worker’s lung (Thermoactinomyces sacchari)

Question 5

Describe the epidemiology of extrinsic allergic alveolitis

Answer 5

UNCOMMON
2% of occupational lung disease
50% of reported cases affect farm workers
Geographical variation

Question 6

List 6 symptoms of acute extrinsic allergic alveolitis

Answer 6

REVERSIBLE episodes of:  
Dry cough   
Dyspnoea  
Malaise   
Fever  
Myalgia  
Wheeze + productive cough may develop if repeat high-level exposure

Question 7

List 4 symptoms of chronic extrinsic allergic alveolitis

Answer 7

Slowly increasing breathlessness
Decreased exercise tolerance
Weight loss
Exposure is usually chronic, low-level + there may be no hx of previous acute episodes

Question 8

Give 3 signs of acute extrinsic allergic alveolitis

Answer 8

Rapid shallow breathing
Pyrexia
Inspiratory crackles: Bi-basal rales (crackles at base of lungs, present during acute HP but not between episodes

Question 9

Give 2 signs of chronic extrinsic allergic alveolitis

Answer 9

Diffuse fine inspiratory crackles (rales)

Clubbing (rare)

Question 10

What bloods should be taken in extrinsic allergic alveolitis?

Answer 10

FBC: neutrophilia, lymphopenia, high ESR, normocytic normochromic anaemia
ABG: reduced PO2 + PCO2
Albumin may be low: but non-specific

Question 11

What investigations are performed for extrinsic allergic alveolitis?

Answer 11

Bloods
ABG
CXR
High Resolution CT-Thorax  
Pulmonary Function Tests  
Diffusing lung capacity of carbon monoxide

Question 12

Why perform serology for extrinsic allergic alveolitis?

Answer 12

Test for IgG to fungal or avian antigens

not diagnostic as may find in normal individuals

Question 13

What may be seen on CXR in extrinsic allergic alveolitis?

Answer 13

Often NORMAL in acute episodes
Acute: fibrosis, upper zone mottling/ consolidation
Hilar lymphadenopathy in rare cases
Chronic: upper zone fibrosis, honeycomb lung

Question 14

What may be seen on high resolution CT in extrinsic allergic alveolitis?

Answer 14

Detects early changes
Chronic: Patchy ‘ground glass’ shadowing + nodules, extensive fibrosis
Used in chronic HP to confirm dx

Question 15

What may be seen on pulmonary function tests in extrinsic allergic alveolitis?

Answer 15

ACUTE: restrictive pattern (low FEV1, low FVC)

SUBACUTE/ CHRONIC: obstructive + restrictive pattern

Question 16

What is seen on Diffusing lung capacity of carbon monoxide in extrinsic allergic alveolitis?

Answer 16

Decreased

may be normal in between episodes of acute

Question 17

Describe disease progression in extrinsic allergic alveolitis

Answer 17

Early dx + prompt allergen removal can halt + reverse disease progression, so prognosis can be good.
With chronic exposure, granuloma formation + obliterative bronchiolitis.

Question 18

When do symptoms start in acute extrinsic allergic alveolitis?

Answer 18

4-12 hrs after exposure