Distinguishing Hypersensitivity Pneumonitis from Idiopathic Pulmonary Fibrosis

Clinical Features

Male sex, age >60 years, and cigarette smoking history strongly favor IPF, with likelihood increasing when these features combine, according to the American Thoracic Society 4, 2
Identifiable antigen exposure that temporally parallels disease onset or activity is the hallmark of fHP, as stated by the European Respiratory Society 2, 5
Any age, any sex, and any smoking status are more heterogeneous than IPF, as noted by the American College of Chest Physicians 2
Inspiratory squeaks on auscultation suggest fHP over IPF, as reported by the British Thoracic Society 6
BAL lymphocytosis >30% strongly suggests fHP, though sensitivity decreases in established fibrosis, according to the American Thoracic Society 7, 6

Basal and subpleural-predominant reticulation with honeycombing defines definite UIP pattern, which is associated with histologic UIP, as stated by the Fleischner Society 6
Probable UIP shows same distribution with traction bronchiectasis but lacks honeycombing, as reported by the Radiological Society of North America 6, 9
Small airways abnormalities with fibrosis suggest fHP, according to the European Respiratory Society 6

fHP demonstrates broader pathologic spectrum than previously recognized, including not just the classic triad but also NSIP pattern, UIP pattern, organizing pneumonia, and airway-centric fibrosis, as noted by the American Thoracic Society 1, 10

Initiate antifibrotic therapy as first-line treatment for IPF, as recommended by the American Thoracic Society 1
Antigen remediation is the critical first intervention for fHP, followed by immunosuppressive therapy, as stated by the European Respiratory Society 1, 8
Antifibrotic agents are considered secondarily only in progressive fibrotic disease, according to the American College of Chest Physicians 1, 2