Diagnosing Asthma

Before labeling a patient as having Asthma, it is important to confirm the diagnosis. How is this best done?

In young children, the history is vital for the diagnosis of asthma. Symptoms include cough, which typically occurs in spasms and is worse at night. Parents frequently report that the child has recurrent colds that last longer than 10 - 14 days. The cough is typically spasmodic to the point of gagging and vomiting. Triggers can include physical activities, laughing and crying (hyperpnea). Wheezing may or may not be present. It is important to have families describe what they mean by wheezing, as many will describe a rattle as a wheeze. A personal history of atopy will also reinforce the diagnosis. For example, a child with eczema, plus or minus food allergies, with onset of recurrent cough and wheeze is more likely to have asthma than a child with cough and no personal history of atopy. A family history of atopy in a child who presents with recurrent cough and wheeze also makes the diagnosis of asthma more likely (Becker et al, Canadian Pediatric Consensus Guidelines, 2003 (updated to December 2004), CMAJ 2005;173(6 suppl): S1-S560). (Level 4 evidence)

Pulmonary function testing is impossible to perform in a standard fashion for children less than 5 - 6 years of age. There are experimental methods to measure pulmonary function in this age group, but they are not commercially available.

In older children or adults, who can perform adequate pulmonary function studies, a 15% increase in the FEV₁, or an increase in FVC representing at least 200 mL of volume, constitutes a significant bronchodilator response suggestive of a diagnosis of asthma. However, some patients with severe airway inflammation do not exhibit a significant bronchodilator response because the underlying obstruction is largely caused by airway inflammation. In these patients, a short trial of corticosteroids to reduce airway inflammation may demonstrate reversibility. Also be aware that if the test is performed when the patient is asymptomatic, a significant change in FEV₁ may not be appreciated.

Peak flow readings may be used in the diagnosis of asthma, but readings must improve by 20% with bronchodilation to be considered significant.

It is important to note that not all children who wheeze have asthma. This is a key concept to understand when diagnosing asthma and it has significant implications for the choice of therapy. There is a group of children who wheeze with colds, but who will improve by age 7 years. These children have no personal or family history of asthma or other atopic disease. The episodes are usually self-limited, lasting for 7 - 10 days. These children do not have asthma.

In addition, children who have had RSV bronchiolitis frequently will wheeze with colds for upwards of 11 years.

- Francine Borduas

Thanks to Alan Kaplan for reviewing the draft copy of this article. Dr. Kaplan is a family physician practicing in Richmond Hill, Ontario. He is Chairperson of the Family Physician Airway Group of Canada

You can search for abstracts of the above references by following this link: PubMed