[Clinical relevance of distal airway involvement in asthma]

Asthma continues to be a global health problem, despite advances in diagnostic techniques and treatment. The inflammatory nature of asthma is currently indisputable, as is the involvement of the entire respiratory tree, both the proximal and most distal airways, which has been demonstrated in multiple studies. The development of the therapeutic arsenal, with more potent drugs and improved inhalation devices, has allowed a certain control to be maintained over the inflammatory process, although the inability to reach the most distal points of the airways has posed a stumbling block that seems difficult to overcome. However, the available information on the real role of distal airway involvement in asthma remains very scarce. Physiopathological evidence shows that, in addition to the large airways, the small or distal airways (those with a diameter of less than 2 mm) substantially contribute to the severity of asthma. Several studies have shown that the inflammatory process seems to be more intense in this area. This finding has been related to nocturnal asthma and an increase in glucocorticoid receptor-beta-expressing cells, associated with corticosteroid-resistant asthma and fatal asthma. Equally, small airway involvement seems to be a highly important factor in asthma in the pediatric age group.