Is it asthma, COPD, or something in between, and does it matter?

Asthma and COPD are the most common obstructive pulmonary diseases of adults. Although differences exist in the genetics, pathogenesis, histopathology, cellular characteristics , and clinical features of these 2 diseases, both disorders are heterogeneous and share a number of features that may be more or less characteristic of one than the other. Because of these overlapping features, as many as 25–50% of older adults have been diagnosed with both of these obstructive disorders. 1 Using data from the National Health and Nutrition Epidemiologic Survey III (NHANES III), Soriano et al reported that 30.2% of survey participants with a self-reported physician's diagnosis of chronic bronchitis and/or emphysema had also been informed by their physician that they had asthma as well. 2 This degree of overlap reflects the frequent difficulty in clinically distinguishing between the 2 diseases. Since no one clinical feature is absolutely discriminatory, and since no validated biomarker has yet been identified that allows one definitively to differentiate asthma from COPD, the diagnosis is dependent on a consideration of several features that may be more characteristic of one than the other disorder. A couple of exceptions include the fact that a defining feature of COPD is " not fully reversible air-flow obstruction, " 3 so that fully reversible air-flow obstruction (namely, a ratio of FEV 1 to FVC Ͻ 70% or less than the lower limit of normal that improves into the normal range in response to a bronchodilator) points to asthma and not COPD, although asthma itself is sometimes not fully reversible. Another exception is very young age, since asthma is usually diagnosed in childhood, whereas COPD is rarely diagnosed under the age of 30 years, with the possible exception of emphysema due to alpha-1 antitrypsin deficiency. On the other hand, asthma may present for the first time in older age, and not infrequently recurs in adulthood after having apparently gone into remission earlier in life. Several other clinical features may help clinicians distinguish between the 2 diseases, although considerable overlap exists. The vast majority of patients with COPD are current or former smokers, but some COPD patients have never smoked, 3 while some asthmatics have a smoking history. Patients with asthma often have a family history of asthma, although familial clustering may also be present with COPD, reflecting the importance of genetic factors in both diseases. While the vast majority of asthma has an allergic basis, 4 some …