Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP) is a heterogenous disease entity characterized by an aberrant immune response to inhalational antigens. Disease modification hinges on early antigen remediation with a goal to attenuate immune dysregulation. Disease severity and progression are mediated by an interface between degree, type and chronicity of exposure, genetic predisposition, and biochemical properties of the inducing agent. Guidelines have provided a standardized approach; however, decision-making remains with many clinical dilemmas. The delineation of fibrotic and nonfibrotic HP is crucial to identify the differences in clinical trajectories, and further clinical trials are needed to understand optimal therapeutic strategies.