CHEST Guidelines-The-Many-Faces-of-Hypersensitivity-Pneumonitis

The-Many-Faces-of-Hypersensitivity-Pneumonitis_che

Pdf Summary

Hypersensitivity pneumonitis (HP) is an immune-mediated lung condition caused by an inhaled antigen, leading to inflammation and/or fibrosis in the lungs. The disease manifests in acute, subacute, or chronic forms, each with distinct clinical and pathologic characteristics. Initially considered rare, chronic HP is now recognized as a more prevalent, albeit confusing, lung disease. The lack of consensus on its definition, diagnosis, and outcomes adds to this complexity.<br /><br />Current classifications differentiate acute HP by short-term intense antigen exposure and systemic reactions. Subacute HP features gradual respiratory symptoms with distinctive radiologic signs like diffuse centrilobular nodularity, while chronic HP often results in slowly worsening breathlessness and respiratory failure, making it similar to other interstitial lung diseases (ILDs).<br /><br />Recent studies, including one by Wang et al., indicate that fibrosis resulting from HP correlates with poorer prognosis compared to cellular nonspecific interstitial pneumonia patterns. However, there's debate over whether pathologic patterns like usual interstitial pneumonia (UIP) or nonspecific interstitial pneumonia (NSIP) substantially impact prognosis, suggesting all fibrotic HP forms fare similarly poorly.<br /><br />The diagnosis of chronic HP is challenging due to the absence of universally accepted criteria. Standard diagnostic tools like biopsy and imaging provide suggestive but not definitive evidence. The lack of an identifiable antigen complicates diagnosis, often relying on a multidisciplinary approach, which has been shown to have limited agreement among experts.<br /><br />For future clarity, it’s suggested to categorize HP by the presence or absence of fibrosis, similar to cellular or fibrotic classification in NSIP. Moving forward, establishing standardized diagnostic criteria for chronic HP is crucial for advancing research and improving patient outcomes.

Keywords

Hypersensitivity pneumonitis

immune-mediated lung condition

inhaled antigen

lung inflammation

chronic HP

interstitial lung diseases

fibrosis

diagnostic criteria

multidisciplinary approach

prognosis