Extrinsic Allergic Alveolitis

Question 1

Definition

Answer 1

Interstitial inflammatory disease of the distal gas exchanging alveoli caused by inhalation of organic dusts. AKA hypersensitivity pneumonia

Question 2

Aetiology

Answer 2

Inhalation of antigenic organic dusts which may b contamined by bacteria or
animal protein leads to a hypersensitivity response (mixed T3 Ag-Ab complex
and T4 granulomatous cellular). This occurs in susceptible individuals following an environmental que:

• Farmers lung: mouldy hay with thermophilic actniomycetes
• Pigeon fancier’s lung: Bloom on bird feathers
• Mushroom orkers lung: compost containing thermophilic actinomycetes
• Humidifier lung: Bacteria containinf water or ameba (Naelgeria)
• Maltworkers lung: Barley or malts containing aspergillus.

Question 3

Epidemiology

Answer 3

Rare. In UK 4/100k py.
50% of these occur on farms. 2% of occupational lung diseases.
Geographical variation due to lobs.

Question 4

Presenting symptoms

Answer 4

Acute: Presents at 4-12h with dry cough, dyspnoea, wheeze, fever and myalgia
(reversible!). Wheeze and productive cough worsen.

Chronic: poorly irreversible manifestation in some, slowly breathless and lower exercise tolderance. May not have history of acute episodes.

Full occupational history, jobs, pets.

Question 5

Signs on physical examination

Answer 5

Acute: rapid shallow breathing, inspiratory wheeze:

Chronic: fine inspiratory basal wheezes. Mat have finger clubbing rarely.

Question 6

Investigations

Answer 6

FBC: neutrophilia, lymphopenia

Serology: Precipitate IgG with antigens from serum/ Not very reliable as they are present in most.

CXR: Often normal. May see upper lobe fibrosis (chronic) or ground glass
appearance.

High res Ct thorax: detects early changes, also shows ground glass shadowing.

Bronchoalveolar lavage: can detect CD8 suppressor T cels.

PFT: FEV1 and FVC both lowered, with normal or high ration (restrictive picture)

Question 7

Management plan

Answer 7

Avoid the trigger. Wear protection masks at work. If this is not possible, wear
protection masks.

Acute: comfort, ansgesia. High dose corticosteroids fastens recovery but not
improves outcome.

Chronic: high dose oral prednisolone.

Regular follow up to monitor function

Question 8

Possible complications

Answer 8

Progressive ung fibrosis due to possible impairment.

Pulmonary fibrosis, pulmonary HTN and RV failure due to the above.

Question 9

Prognosis

Answer 9

Acute form resolves if further exposure is prevented.