OTTAWA - Up to 30 per cent of Canadians diagnosed with asthma may not actually have the chronic, and sometimes deadly condition, according to the surprising findings of a study appearing Tuesday in the Canadian Medical Association Journal.
Researchers examined 496 asthma patients from eight cities across the country and through clinical testing and the withdrawal of medications, they determined that 150 of them had no evidence of the disease. Some of the patients had been living with what they thought was asthma for more than 15 years, and taking medication to treat it. It is possible, though not common, for some people to "outgrow" asthma, said Dr. Shawn Aaron, the lead researcher.
"I think what's happening is that patients are walking into the physician's office complaining of shortness of breath, coughing, wheezing and the physician is making the diagnosis based on the symptoms but not confirming the diagnosis with a test," said Aaron, a senior scientist at the Ottawa Health Research Institute which conducted the study.
Asthma can be accurately diagnosed in most cases with a simple test called spirometry which measures the airflow through a person's lungs, yet other research indicates that half of patients whose doctors diagnosed them with asthma were never given the test.
It isn't clear why doctors don't automatically order the test for patients they suspect of having asthma - it's a non-invasive and inexpensive test that can be done at a laboratory, or in the doctor's office with the proper equipment and training.
Aaron suspects in some cases, doctors deliver an instant diagnosis with an instant fix that satisfies patients in the short-term. "But in the long-term, I think we're doing them a disservice," he said.
In addition to being labelled with a chronic disease they don't have, a misdiagnosis of asthma can have other physical, and financial, consequences for patients. Asthma drugs can cost anywhere from $60 to $150 per month and their long-term side-effects can include osteoporosis, glaucoma, and cataracts. A misdiagnosis also means patients haven't discovered the true cause of their symptoms.
Most of the patients in the study were grateful to learn they did not have asthma, said Aaron, but a handful refused to believe they were misdiagnosed and continued to take their medication.
Aaron stressed that the majority of the people in the study did have asthma and needed to take medication for it.
The main message that can be drawn from the results is that if patients were diagnosed without a spirometry test, they should ask their doctor for one, said Aaron. "If you think you don't have asthma but you have been labelled with it and you are taking asthma medicines, see your doctor," said Aaron. "But do not stop your medicine before seeing your doctor."
A CMAJ editorial on the study says such misdiagnosis highlight "a major problem in our system of asthma care."
The original purpose of the study was to see if obese people were more likely to be misdiagnosed with asthma, but the results determined that misdiagnosis was just as common in people of normal weight.