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Wednesday, April 8, 2015

The prevalence of severe refractory asthma

Severe asthma is characterized by difficulty to achieve disease control despite high-dose inhaled glucocorticoids plus long acting β2 –agonists (LABAs) or oral corticosteroids (OCSs). In 2011, the Innovative Medicine Initiative (IMI) published an international consensus statement in which a more accurate definition of severe asthma was proposed. In this statement, a clear distinction was made between “difficult to control asthma” and “severe refractory asthma.” In patients with difficult to control asthma, the lack of asthma control is due to other factors than asthma itself, such as nonadherence to treatment or incorrect inhalation technique. On the other hand, in patients with severe refractory asthma, the disease remains uncontrolled despite addressing and removing all possible factors that might aggravate the underlying disease. Hekking et al sought to estimate the prevalence of severe refractory asthma as defined by the IMI consensus (J Allergy Clin Immunol 2015; 135(4): 896-902).

Adult patients with a prescription for high-intensity treatment were extracted from 65 Dutch pharmacy databases, representing 3% of the population. Questionnaires were sent to patients and about half (2312) were analyzed. The diagnosis of asthma and degree of asthma control were derived from the questionnaires to identify patients with difficult-to-control asthma and inhalation technique was assessed in a random sample of 60 adherent patients. The authors determined that patients with difficult to control asthma, adherence to treatment, and a correct inhalation technique were qualified as having severe refractory asthma. The results indicated that of asthmatic adults, 3.6% qualified for a diagnosis of severe refractory asthma, representing 10.4 patients per 10,000 inhabitants.

The authors speculate about the reasons for the difference between the prevalence of severe refractory asthma mentioned in the literature (5%-10%) and their results (3.6%). Estimations in the literature are based on expert opinion and clinical experience, it is reasonable to believe that not all factors that negatively influence asthma control are receiving full attention in the consulting room. Therefore clinical overestimation of the prevalence of truly severe refractory asthma might easily occur because of misclassification of patients with difficult-to-control asthma as patients with severe refractory asthma. Clinicians should be aware of the distinction between these 2 conditions and check potential aggravating factors, in particular poor adherence with treatment and inadequate inhalation technique. Another important result of this study is because the prevalence of this condition might be lower than previously thought, severe refractory asthma could fulfill the criteria of a rare disease and qualifies for niche drugs. Together, these data will hopefully facilitate the development and reimbursement of novel targeted treatments. 

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