This patient has had a drop of lung function in the last months, particularly with a sustained drop of the FEV1 in more than 20%. The HRCT has corroborative findings that support bronchiolitis obliterans: diffuse air-trapping and mosaic perfusion appearances.

The left lung shows diffuse architectural distortion and volume loss consistent with the known pulmonary fibrosis. 

Bronchiolitis obliterans is the most common form of chronic lung allograft dysfunction (CLAD), accounting for about three quarters. Also, studies have shown that about 50% of post-lung transplant patients develop BOS within 5 years ¹.