# Hypersensitivity Pneumonitis

Extrinsic allergic alveolitis - to inhaled organic small particles. 

Recent guidelines:

CHEST: https://journal.chestnet.org/article/S0012-3692(21)00686-3/fulltext

ATS: https://www.atsjournals.org/doi/10.1164/rccm.202005-2032ST

ARUP's panel and what the significance of each result is: 

![alt](https://photos.collectednotes.com/photos/5187/200a7dbe-8a3d-4fad-8c21-96b5118ae8b9)

Nonfibrotic: 

![alt](https://photos.collectednotes.com/photos/5187/6e91d6df-1bd2-4ee0-88e5-d93ce65f487b)

Fibrotic:
![alt](https://photos.collectednotes.com/photos/5187/272e9096-095f-408b-8837-605c2de59229)


Diagnostic algorithm (From ATS)

![alt](https://photos.collectednotes.com/photos/5187/0fb15d68-dd72-41e1-a9fb-6aa26c076289)

40% BAL lymphocytosis is strongly associated. 


Treatment: 

- Antigen removal (worse prognosis if no antigen is identified - Noguieria et al Pulmonology 2019) 
- Steroids, but weak evidence base (RCT of 36 resulted in improvement in DLCo and FVC at 1 month but no difference at 5 years; matched cohort of 144 showed slower fibrosis progression on CT - esp early fibrosis)
- AZA, MMF - need to exclude IPF (increased mortality). Less side effects than long-term steroids. 
- ? Nintedanib - INBUILD study, progressive fibrosis including 26.1% who had chronic HP