As many as one-third of asthma patients age 16 and over may not actually have the chronic disease, according to a study published Nov. 18 in the Canadian Medical Association Journal.
In a study initially designed to assess misdiagnosis rates of asthma among obese people a population that prior studies suggest suffers more often and more severely from the disease researchers at the University of Ottawa discovered that doctors may be overdiagnosing asthma in all patients, regardless of weight, by some 30%. "We were bowled over by these results," says Dr. Shawn Aaron, the study's lead author and head of respiratory medicine at the University of Ottawa. (See TIME's A-Z Health Guide.)
The analysis included 540 patients in Canada who were recruited by telephone survey. All patients had been previously diagnosed with asthma and were prescribed medication to control their symptoms. Over the course of up to four lab visits and a battery of pulmonary tests, which included examining how well patients fared when their asthma medications were tapered off or taken away, researchers confirmed the diagnosis in 346 patients, or 70%. But for 150 patients who accounted for 31.8% of obese participants and 27.8% of their normal-weighted peers their initial diagnosis was wrong. Indeed, says Aaron, many of these patients may have already suspected as much; about 25% of the patients in whom researchers excluded asthma had not been taking their daily asthma medication a factor that Aaron concedes may have prompted some patients to enroll in the study. "They are recognizing that the medicines aren't working for them, so they're not taking them as prescribed," says Aaron.
The study's findings come as no shock, says Dr. Norman Edelman, chief medical officer for the American Lung Association. The symptoms of wheezing and shortness of breath, which frequently get confused for asthma, may signal a host of other health problems, including the a respiratory infection, chronic obstructive pulmonary disorder, anxiety and congestive heart failure. In fact, congestive heart failure is so often misdiagnosed as asthma that lung experts often refer to it as "cardiac asthma," Edelman says. "All that wheezes is not asthma."
The dangers of misdiagnosing a patient's true condition are obvious. There are also potential risks of treating a nonexistent illness. Currently, more than 300 million people have asthma worldwide, with another 100 million patients anticipated by 2025. Unnecessarily treating people may have no impact at best, but it costs patients money and, worse, may expose them to harmful side effects for years or even decades. "The commonest medicines that we use are inhaled steroids," says Aaron. "They are very safe for patients with asthma, but are associated with long-term side effects, including osteoporosis, glaucoma and cataracts." The drugs may also exacerbate the patients' actual disorder anxiety, for example for which patients may continue to fail to seek treatment.
Still, Aaron is quick to point out that even if patients suspect they have been misdiagnosed, they should stick with their medication until they consult their doctor. "I don't want patients to stop taking their medicine cold turkey," he said, emphasizing that the patients who ultimately went off their asthma drugs in his study did so over a period of several months while undergoing continuous tests to confirm the exclusion of asthma.
The solution to overdiagnosis, says Aaron, is simple: consistent, objective testing to identify asthma more accurately. A spirometry test, for example, measures the rate and volume of airflow during the patient's exhale, before and after using an inhaler. "If you came in with chest pain, [the physician] would do an electrocardiogram. If you came in complaining of high cholesterol they would do a blood test. But we're not measuring asthma before we start to throw medicines at it. We're making the diagnosis on spec, as it were."
But there is an established and often successful history in medicine of diagnosis by treatment. Says Edelman so-called "therapeutic trials" of asthma medication may be appropriate, based on a patient's symptoms and medical history even without pulmonary tests. "If a 12-year-old kid comes into your office and says he wheezes every time he goes near his friend's dog, and you give him an inhaler and it never happens again, that's a therapeutic trial," he says.
The real mistake happens later, according to Edelman, when the initial trial fails and the physician doesn't rethink the diagnosis or run the proper tests and instead addresses the problem by using different drugs. "We need to pay attention to what symptoms mean and patients' response to treatment. We cannot accept lack of responsiveness to medication. It could be a misdiagnosis," Edelman says.
Misdiagnosis goes both ways, however. Underdiagnosis and undermedication of asthma can also be dangerous and even life-threatening, according to Edelman: "There are still 4,000 deaths each year, mostly from underdiagnosis."
The best advocates for patients diagnosed with asthma are the patients themselves, says Aaron. If you suspect that you may have been misdiagnosed, ask your doctor to run some pulmonary tests or pursue a different course of treatment. As Aaron says, "The danger of misdiagnosis is that it's a missed opportunity to figure out what's truly wrong with the patient."