Approach

The most important element in any allergic lung disease is avoidance of the causative antigen.

In the case of occupational exposure, removing the individual from the exposure generally means workplace reassignment. However, environmental interventions such as reducing humidity and improving ventilation may result in a low enough antigen exposure to avoid the need for reassignment.

In the case of non-occupational exposure, environmental intervention is generally the best solution; examples include cleaning out the mouldy crawl space (a type of basement in which one cannot stand up).

Pharmacotherapy

There are few studies of the pharmacological therapies for hypersensitivity pneumonitis (HP). Oral corticosteroids are usually instituted where symptoms of HP present acutely because there are reports of improvements in both symptoms and pulmonary function. With concomitant antigen avoidance, after 1-2 weeks’ therapy the corticosteroids can usually be tapered off over about 6 weeks.

Treatment of chronic HP is not well established due to lack of clinical trials. The approach is therefore generally based on observational data and expert opinion.[47]​ Patients with chronic fibrotic HP are often given corticosteroids, especially if there is evidence of inflammation such as bronchoalveolar lavage lymphocytosis or ground glass opacities.[43][47][57][58]​​ An immunosuppressant such as azathioprine or mycophenolate may be started in patients with a suboptimal response to corticosteroids, or in patients who have a moderate to high corticosteroid dose requirement.[47]​ After starting the immunosuppressant, the corticosteroid dose is generally tapered, and then maintained at a low dose. Observational studies suggest that immunosuppressants can improve lung function and reduce corticosteroid dose with patients with chronic or fibrotic HP, but randomised clinical trials are needed.[59][60][61][62]

Supportive measures

There are several supportive measures that need to be considered to improve quality of life and mitigate factors that contribute to disease progression.

  • Patients who continue to smoke cigarettes should be counselled to quit.

  • Patients may benefit from pulmonary rehabilitation programmes to improve their functional status and quality of life.[63]​​[64]​​

  • Severe hypoxaemia (PaO₂ ≤55 mmHg or oxygen saturation ≤89%) at rest or with exertion should be managed with supplemental oxygen. This is strongly recommended by the 2020 American Thoracic Society guideline on home oxygen therapy for adults with chronic lung disease.[65][Evidence C]

Lung transplantation

As for patients with other interstitial lung diseases, lung transplantation may be considered in eligible patients with progressive fibrotic disease.[1][66]

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