This is an article from the Jan-Mar 2011 edition of the Annuls of Thoracic Medicine. It makes several interesting points about asthma. I hadn't heard the term "DTA" Difficult-to-Treat Asthma before but it is appropriate!
In the first paragraph -
" . . . Nongenuine causes can be further divided into three categories: (1) misdiagnosis where the problem is not bronchial asthma to start with, but another respiratory system pathology that is not appropriately addressed, e.g. bronchiectasis, endo-bronchial tumors, and vocal cord dysfunction, (2) comorbidity that worsen bronchial asthma and making it difficult to manage, e.g. chronic sinusitis, gastro-esophageal disease, sleep apnea syndrome, and congestive heart failure . . . "
Another paragraph from the article -
"Asthmatic patients with persistent symptoms despite adequate maintenance therapy should be systematically evaluated to identify factors contributing to the poor control and then adopt a targeted intervention scheme.[,] This includes a through history to identify precipitating factors, home or work allergens, compliance with medications, nature of their illness, and any other relevant issues. A complete physical examination for the chest and the rest of the body is to be done to explore other comorbidities such as the presence of signs of bronchiectasis, interstitial lung disease, CHF, and joint disease. Laboratory tests include complete blood count, serum levels of IgE, schistosoma serology, screening for liver and kidney diseases, and other inflammatory biomarkers if relevant and available. Radiological tests include chest radiography, computerized chest, and sinuses scans. Other investigations are requested according to the clinical situation and differential diagnosis."
I wasn't sure exactly what "comorbitity" is so I found this definition on the Merriam-Webster online dictionary –