Clinical and radiologic manifestations of hypersensitivity pneumonitis.

Hypersensitivity pneumonitis (HP) is an inflammatory interstitial lung disease caused by recurring exposure to a variety of occupational and environmental antigens. It features widely variable clinical, radiologic, and histopathologic findings. Because the clinical findings of HP mimic multiple other diseases, a high degree of clinical suspicion and a thorough occupational and environmental history are essential for accurate diagnosis. There is no single pathognomonic feature for HP; rather, diagnosis relies on a constellation of clinical, radiologic, and pathologic findings. The radiologic manifestations, particularly the high-resolution computed tomography (HRCT) pattern, provide important clues and frequently point clinicians towards the correct diagnosis. The HRCT findings in HP may include ground-glass opacification, centrilobular nodules, air trapping (mosaic pattern), fibrosis, emphysema, or more frequently a combination of these. The combination of a mosaic pattern with ground-glass opacification and centrilobular nodules is particularly suggestive of the diagnosis. The best long-term prognosis is achieved with early diagnosis and removal from exposure.