[The diagnostic approach to difficult-to-treat asthma and severe asthma].

Difficult-to-treat asthma refers to asthma that is not controlled despite high or medium doses of inhaled steroids or in which high doses of treatment are required to maintain an adequate control of the symptoms and to reduce the risk of exacerbations. An inadequate technique to use the inhaler, poor adherence to treatment, smoking, comorbidities, or an incorrect diagnosis should be considered. In severe asthma, despite adherence to treatment with optimized maximum doses and the management of factors that could contribute, multiple medications in maximum doses are required to have an adequate therapeutic control or this is not achieved. The approach to these patients involves a meticulous process due to the multiple factors that can influence poor asthma control and that can lead to a misclassification of the disease when, in reality, the patient can be presenting different comorbidities whose treatment could decrease the severity of asthma symptoms and modify the prognosis. The objective of this document is to make the approach to patients with difficult-to-treat asthma and severe asthma known, as well as the most frequent comorbidities. A search was made in PubMed with the purpose of identifying the main pathologies that may be present in patients and, based on what is described in the literature, to propose a diagnostic approach. 100 studies were comprised in this review, including clinical guidelines such as GINA, GEMA, and ERS/ATS.