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118 Chapter 3: Respiratory system

bacterial infection. Classical signs are clubbing, cyanosis development of cor pulmonale. Single-lung transplant
and fine end-inspiratory crackles in the mid to lower has been shown to be viable, but most patients have
lungs. concomitant disease which precludes this.

Microscopy Prognosis
Characteristically chronic fibrotic, scarred zones with Median survival of 5 years. Forty per cent die of progres-
collapsed alveoli and honeycombing alternate with ar- sive respiratory failure, most of the others from acute in-
eas of relatively unaffected lung. Where there is acute fection or concomitant ischaemic heart disease. Newer
injury, there are foci of activated fibroblasts with little anti-fibrotic and immunological therapies are being in-
inflammation. vestigated.

Complications
The disease is progressive and usually unresponsive to Extrinsic allergic alveolitis
treatment, and patients develop respiratory failure, pul- Definition
monaryhypertensionandcorpulmonale.Anacuteform An immune reaction within the lung to inhaled organic
exists (Hamman–Rich syndrome or acute interstitial dusts.
pneumonia) with a very high mortality rate.

Aetiology
Investigations
See Table 3.14
Chest X-ray shows fine reticular shadows, mainly in

the bases and peripheral honeycombing.
Pathophysiology
CT scan of the chest show a ground glass appearance

1 Afterexposure there is formation of antibody–antigen
in areas of alveolitis with extensive reticular patterns
complexes. Normally immune complexes are cleared
due to fibrosis.
but if they persist, they activate the complement sys-
Respiratory function tests shows a restrictive pattern

temresultinginlocalinflammation,inflammatorycell
with reduced lung volumes, FEV 1 and FVC are low but
recruitment and cellular damage (i.e. a type III hyper-
the ratio of the two is normal/high, and gas transfer
sensitivity reaction).
is reduced. In smokers there may be a superimposed
2 If there is repeated exposure a type IV cell mediated
obstructive pattern.
hypersensitivity reaction occurs with the formation
Blood gases show hypoxaemia with normal or low

of small granulomas. The lung damage is repaired by
carbon dioxide levels.
pulmonary fibrosis.
High erythrocyte sedimentation rate (ESR) in up to

one third of patients.
Broncho-alveolar lavage shows increased cells partic-
Table 3.14 Causes of extrinsic allergic alveolitis
ularly neutrophils.
Disease Source Antigens
Lung biopsy is indicated if possible, usually trans-

Farmer’s lung Mouldy Micropolyspora
bronchial via bronchoscopy. Because of the patchy
hay/vegetable faeni,
nature of the disease, however, surgical lung biopsy material thermophilic
of several sites may be needed. actinomycetes
Mushroom Mushroom dust Thermophilic
Management picker’s lung actinomycetes
Bird fancier’s lung Avian excreta Various proteins
There are no proven effective treatments. A trial of pred- and feathers
nisolone 30 mg is indicated if the diagnosis is not well Malt worker’s Germinating Aspergillus
established in case there is a responsive interstitial pneu- lung barley clavatus
monitis. Azathioprine and ciclosporin have also been Humidifier fever Contaminated Various bacteria
humidifiers and/or
tried. Supportive treatment includes oxygen, long-term
amoebae
oxygen therapy improves the prognosis by delaying the