To the Editors:
We read with great interest the new clinical classification of pulmonary hypertension (PH) 1, that represents a tremendous and successful effort to summarise the existing evidence of a rapidly evolving field in a physician-friendly manner. We want to focus on the inclusion of sarcoidosis, pulmonary Langerhans cells histiocytosis (PCLH) and lymphangioleiomyomatosis (LAM) in the subgroup of PH with unclear or multifactorial aetiologies (Group 5). Although raising such an issue might seem pedantic, we believe that there are good reasons for reconsidering the group place of these disorders.
Interstitial lung diseases (ILD) consist of disorders of known (e.g. collagen vascular disease, environmental, drug-induced) as well as unknown causes. The latter include idiopathic interstitial pneumonias, granulomatous lung disorders (e.g sarcoidosis), and other forms of ILDs, including LAM, PLCH and eosinophilic pneumonia 2.
Group 5.2 diseases may have a systemic component but their pulmonary manifestations far outnumber the manifestations of any other system. They mainly represent diffuse parenchymal lung diseases with distinctive and well-defined clinicopathological features that can affect all aspects of lung anatomy (interstitium, airspaces, peripheral airways and vessels), resulting in PH in a proportion of patients. Sarcoidosis presents with associated lung involvement in up to 95% of cases 3 and respiratory failure is the most common cause of death in Europe and the USA. Furthermore, mean pulmonary artery pressure has been significantly correlated with diffusion deficit and pulmonary vascular resistance with arterial oxygen tension in this setting 4. PCLH is an ILD, preferentially affecting heavy smokers. LAM usually presents with cystic degeneration of the lungs and is often misdiagnosed initially as asthma or chronic obstructive pulmonary disease. It is a fact that the pathogenesis of PH for these disease entities is incompletely understood and may be multifactorial, but the same is true for all other ILDs 5. Not surprisingly, no PAH-specific therapies have been approved for all these disease entities.
Indeed, the current classification moves to the right direction by adopting a clinically meaningful way of thinking and avoiding unnecessary pathophysiological implications; PH owing to left heart disease (Group 2) and chronic thromboembolism (Group 4) are good examples. In this context, sarcoidosis, PLCH and LAM (Group 5.2) represent disorders that, according to the current evidence, are associated with PH mainly due to lung involvement and, therefore, we propose their inclusion in the third category (PH owing to lung disease and/or hypoxia) in any future classification scheme.
Statement of interest
None declared.
- © ERS Journals Ltd
