Difficult-to-control asthma in adults.

Difficult-to-control asthma in adults is under-diagnosed and under-treated in the United States, particularly in those 40 years of age or older. Increasing attention has been focused on the subset of adult patients with poorly controlled asthma because they consume up to 85% of all health care dollars spent on asthma, while representing 20% of all asthma patients. In this article, we define difficult-to-control asthma and discuss the problem of misdiagnosis.