Objective: To characterize clinical phenotypes of severe asthma. Methods: A total of 111 patients were retrospectively evaluated at a specialized outpatient clinic. A systematic protocol for patient evaluation and follow-up was applied. Treatment compliance and control of the disease at the end of follow-up were defined by clinical and functional data. Patients who did not meet asthma control criteria after six months despite compliance with treatment and correct use of medication were characterized as treatment-resistant. Phenotypes were determined by factorial analysis and compared using various tests. Results: At the end of follow-up, 88 patients were considered treatment compliant and 23 were considered noncompliant. Factorial analysis of the compliant patients identified four phenotypes: phenotype 1 (28 patients) comprised patients who were treatment-resistant, more often presenting nocturnal symptoms and exacerbations, as well as more often using rescue bronchodilators; phenotype 2 (48 patients) comprised patients with persistent airflow limitation, lower ratios of forced expiratory volume in one second/forced vital capacity at baseline, more advanced age and longer duration of symptoms; phenotype 3 (42 patients) comprised patients with allergic rhinosinusitis who were nonsmokers and presented predominantly reversible airflow obstruction; and phenotype 4 (15 patients) comprised cases with a history of aspirin intolerance to acetylsalicylic acid associated with near-fatal asthma. Conclusions: A significant number of patients with severe asthma are noncompliant with treatment. Although many patients with severe asthma have persistent airflow obstruction, the most relevant clinical phenotype comprises patients who are resistant to the typical treatment.

Keywords: Asthma; Asthma/prevention & control; Asthma/treatment.