chronic hypersensitivity pneumonitis

A chronic progressive form of pneumonitis which occurs after exposure to a variety of antigens, including occupational antigens (i.e. farmer's lung, pigeon breeder's lung, byssinosis etc.). Pathology: 1) granulomatous reaction with round cell infiltrates, epithelioid cells 2) septal swelling with lymphocytes & plasma cells 3) foamy macrophages with interstitial granulomas (pigeon breeder's lung) Clinical manifestations: 1) symptoms are insidious in onset 2) symptoms are progressive eventually resulting in pulmonary fibrosis 3) clinically identical to idiopathic pulmonary fibrosis Laboratory: 1) bronchoalveolar lavage (BAL) may show reversal of CD4/CD8 ratio 2) lung biopsy 3) positive serology is not diagnostic a) 20% of asymptomatic farmers have positive precipitins b) 40% of asymptomatic pigeon breeder's have positive precipitins c) 10% of symptomatic farmers have negative precipitins Special laboratory: Pulmonary function testing: 1) decreased lung volumes 2) decreased lung compliance 3) decreased DLCO 4) exercise-induced hypoxemia Management: 1) avoid exposure to causative precipitins 2) corticosteroids

General

hypersensitivity pneumonitis; extrinsic allergic alveolitis; pigeon breeder's lung; bird fancier's lung; farmer's lung; allergic pneumonitis chronic lung disease

References

Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 759-60