The current World Health Organization (WHO) classification of pulmonary hypertension (PH) categorises PH due to chronic lung disease under group 3 [1]. There are many reports of PH complicating the course of the more common interstitial lung diseases (ILD), such as idiopathic pulmonary fibrosis (IPF), connective tissue disease associated-ILD and conditions within WHO group 5, such as sarcoidosis. What is surprising though is the relative paucity of data on PH complicating the course of other forms of ILD. The study in this issue of the European Respiratory Journal by Oliveira et al. [2] is the largest to date of right heart catheterisation (RHC) documented PH associated with chronic hypersensitivity pneumonitis (CHP). The authors documented the presence of PH in 50% of their cohort, most of whom (22 out of 25) had group 3 PH, with the three remaining patients having evidence of group 2 PH. Similarly to IPF, they found that the presence of PH was associated with worse functional impairment [3].
This study raised a number of important issues. The first point of interest does not pertain to PH, but rather the broad spectrum of ILD. Specifically, the authors evaluated 1023 consecutive patients with ILD, of whom 95 were documented to have CHP. This equates to a prevalence of just below 10%, which is informative to the ILD community; although, this prevalence is likely to vary regionally and internationally based on many economic, environmental and cultural differences. The somewhat high prevalence of PH is in keeping with what has been described previously in IPF …