Chronic hypersensitivity pneumonitis: important considerations in the work-up of this fibrotic lung disease

Abstract

Purpose of review: Chronic hypersensitivity pneumonitis is increasingly recognized as an important mimic of other fibrotic lung diseases. This review will summarize recent data regarding the importance and difficulty of determining causative exposures both for accurate diagnosis and prognosis, and describe the expanded pathologic spectrum of the disease, the effects of fibrosis on prognosis and challenges in the diagnostic evaluation.

Recent findings: Several recent publications show the potential pathologic patterns induced by chronic hypersensitivity pneumonitis are broader than the classic triad of bronchiolitis, interstitial infiltrates and granulomas. Other pathologic patterns include nonspecific interstitial pneumonia, usual interstitial pneumonia, organizing pneumonia, bronchiolitis and airway centric fibrosis. Detecting a causative antigen in fibrotic hypersensitivity pneumonitis is challenging but critically important both for accurate diagnosis and improved prognosis. The prognosis in hypersensitivity pneumonitis worsens in the presence of fibrosis, but it remains significantly better than idiopathic pulmonary fibrosis.

Summary: Hypersensitivity pneumonitis is increasingly recognized as an important cause of fibrotic interstitial lung disease. Hypersensitivity pneumonitis demonstrates a remarkable tendency to mimic other idiopathic interstitial pneumonias. A detailed exposure history remains a cornerstone of diagnosis and management.