Abstract
Awareness of hypersensitivity pneumonitis (HP) as a unique disease entity dates back to the 18th century. Since then, numerous inciting agents have been attributed to inducing HP, and the pathogenesis of the disease is now better understood.
HP is a disease of many facets and phenotypes, making its recognition and differentiation from other interstitial lung diseases (ILDs) challenging, in particular idiopathic pulmonary fibrosis (IPF). The clinician is often unable to distinguish features of chronic HP (CHP) from those of IPF, and some patients meeting the 2011 criteria for the diagnosis of IPF may in fact have CHP with pulmonary fibrosis.
The high rate of screen failures in patients participating in IPF clinical trials highlights this diagnostic challenge, as pulmonologists may be misdiagnosing patients with CHP as having IPF, overlooking environmental factors that can contribute to the disease. Despite recent data and reports suggesting new directions in the diagnosis, management, and treatment of HP, there remain substantial gaps in knowledge of epidemiology, pathogenesis, optimal diagnostic approach, and, ultimately, classification of this disease.
Consensus among experts for diagnosis, treatment, and management are lacking, and the need for consensus guidelines is evident. In this Perspective, we propose diagnostic criteria and a novel classification of HP based on a combination of international clinical experience and available evidence.
We believe that these criteria will be of use to the pulmonologist when confronted with patients suspected of having HP and promote further study to increase our understanding of how HP should be managed. The proposed criteria need to be validated in further studies, and therefore should not be interpreted as a guideline recommendation.