Asthma is a specific lung disease that is different from emphysema and chronic obstructive bronchitis. COPD is often used as a kind of shorthand to describe emphysema, chronic obstructive bronchitis, or a combination of both. COPD always refers to diseases that are not asthma. The COPD group of lung diseases is not related to asthma, although emphysema and chronic obstructive bronchitis exhibit similarities to asthma, reviewed in the next answer. Confusion seems to arise under several circumstances. In the first case, COPD can co-exist with asthma, typically in an older adult with a history of cigarette smoking, and both conditions are present together.
Secondly, some medical practitioners in a blatant misuse of language use the word asthma to refer to the breathlessness characteristic of the COPD group of lung diseases. They tell their patients with pure emphysema or chronic obstructive bronchitis that they have “a touch of asthma” rather than explaining that the symptom of shortness of breath is a fundamental manifestation of the COPD. Finally, COPD and asthma are treated with inhaled medications, some of which are effective in both conditions. On occasion, two family members or friends with two different diagnoses may (correctly) be prescribed the same inhaler, and that can lead to all kinds of assumptions.
I am reminded of a 75-year-old in my care; he had smoked heavily and had marked emphysema. He had succeeded in kicking his former cigarette habit, an achievement of which he and I were very proud. He was naturally quite concerned about the emphysema diagnosis. He explained to me that he was particularly troubled about what his prognosis and quality of life would become over time. Over the course of a year, I prescribed several medications for treatment of his emphysema and he would see me in the office every few months for follow-up. On one memorable visit, he arrived in excellent spirits and shared the news that his 21-year-old grandson who had been diagnosed with asthma at the age of 6 was in town and staying over for a weekend visit. On that visit, my patient discovered that he was taking the identical inhaled medication that his grandson used for asthma, and announced grinning from ear to ear, “Well, Doc, I figured out then that you’re treating me not only for emphysema, but for asthma, too, and that means my prognosis isn’t that bad . . .”