An update on hypersensitivity pneumonitis: what a clinician wants to know

A recent international collaboration has updated the clinical definition and diagnostic recommendations for hypersensitivity pneumonitis, focusing on fibrotic and non-fibrotic phenotypes. However, how these transfer to clinical practice and their impact upon clinical management and prognosis of hypersensitivity pneumonitis is unclear. This review will focus on recent advances in the understanding of the clinical aspects of hypersensitivity pneumonitis, predominantly its epidemiology, diagnosis, classification and treatment.

Hypersensitivity pneumonitis is a rare disease within the general population, with variable geographical incidence because of environmental, cultural and occupational factors. Confidence in diagnosis relies upon the presence of clinical features with a temporal relationship to an associated exposure, radiological and histopathological features, bronchiolo-alveolar lavage lymphocytosis and precipitating antibodies/specific immunoglobulin G to antigens. Although emerging evidence regarding nintedanib use in progressive fibrotic interstitial lung disease is promising, the majority of therapies (corticosteroids and immunosuppressive agents) used traditionally in hypersensitivity pneumonitis lack a robust evidence base.

With a clear definition of fibrotic and nonfibrotic hypersensitivity pneumonitis phenotypes now established, clinical research trials (predominantly randomized controlled trials) should clarify and resolve the discussion regarding antigen avoidance, corticosteroid therapy, immunosuppressive therapy and antifibrotic therapy in fibrotic and nonfibrotic subtypes of hypersensitivity pneumonitis.