Background: Hypersensitivity pneumonitis (HP) is an immune-mediated interstitial lung disease resulting from repeated inhalation of environmental antigens, most commonly in occupational settings. Chronic exposure may lead to progressive fibrotic lung disease, often mimicking idiopathic pulmonary fibrosis (IPF), resulting in delayed diagnosis and suboptimal management.

Case Presentation: We report a case of a 48-year-old male farmer who presented with progressive exertional dyspnea over 18 months. He had a significant occupational exposure history of daily contact with moldy hay and grain dust for more than 25 years. Clinical examination revealed tachypnea, resting hypoxemia, and bilateral end-inspiratory crackles predominantly in the upper lung zones. There was no history of smoking, fever, weight loss, or hemoptysis. Based on the characteristic exposure history, clinical features, and examination findings, a diagnosis of chronic hypersensitivity pneumonitis was strongly suspected.

Discussion: This case highlights the insidious nature of chronic HP and the critical role of detailed occupational and environmental exposure assessment in patients presenting with unexplained progressive dyspnea. Chronic HP frequently overlaps clinically and radiologically with other fibrotic interstitial lung diseases, particularly IPF, but differs significantly in etiology, management, and prognosis. Early recognition, antigen avoidance, and appropriate therapeutic intervention are essential to prevent irreversible pulmonary fibrosis.