Pulmonary hypertension associated with nonparenchymal restrictive lung diseases

Prior to 2024, pulmonary hypertension (PH) associated with chronic lung diseases (group 3 in the classification of PH) was subclassified according to the type of ventilatory disorder (obstructive, restrictive lung disease or mixed patterns) and not according to the lung disease itself. In 2024, the 7th World Symposium on PH proposed a revised classification, describing associations with specific lung diseases, such as COPD, interstitial lung disease and combined pulmonary fibrosis and emphysema. This update highlights the distinct pathophysiological mechanisms, clinical manifestations, outcomes and management strategies across these subgroups. Of note, a nonparenchymal restrictive lung disease subgroup has been identified, which includes patients with hypoventilation syndromes (due to kyphoscoliosis, diaphragmatic diseases, obesity hypoventilation syndrome, central hypoventilation syndromes, etc.) or pneumonectomy. Paradoxically, despite being one of the earliest forms of PH described, PH associated with nonparenchymal restrictive lung diseases remains among the least studied subtypes. As with all causes of group 3 PH, the primary focus of management is to address the underlying condition whenever possible. There are few data on the efficacy, safety and tolerability of the treatments approved for pulmonary arterial hypertension in this specific population. This review aims to provide updates on this condition and its management, to highlight the mechanisms of PH in each nonparenchymal restrictive lung disease and to study the relevance of the new classification and the necessary avenues of research.