Almost two out of three children with severe asthma are boys. But women account for more than two out of three adults with severe asthma. And no one really knows why. Those are some of the most striking results of a cross-sectional study of severe asthma by researchers from National Jewish Medical and Research Center being published in the October issue of the journal Chest. The research team, led by Joseph Spahn, M.D., also found that children with severe asthma had surprisingly good airflow in and out of their lungs, which could lead to misdiagnosis and undertreatment of seriously ill patients.
"Our findings highlight many of the significant differences between severe asthma in children and adults," said Dr. Spahn. "We hope they will spur further research that can lead to a better understanding and better treatment of this disease."
People with severe asthma, whose asthma remains uncontrolled in spite of high doses of medication, represent 5 percent to 10 percent of the estimated 20 million asthma patients in the United States. But they are important in terms of suffering, medical costs and difficulty finding effective treatments. Dr. Spahn and his colleagues examined a variety of demographic and biological data for 275 patients with severe asthma who had been referred to National Jewish.
Physicians have suspected that severe asthma differs considerably from childhood to adulthood, and indeed that turned out to be the case. The greatest difference was the male-to-female ratio. Males accounted for 62% of the patients under age 18. But 68% of the severe asthma patients over 18 were female. A similar situation has been noted in mild and moderate asthma, but not in patients with severe asthma.
"There has been speculation that a woman's hormones or possibly a difference in the size of male and female lungs play a role in this changing pattern of asthma prevalence, but no one really knows for sure why it occurs," said Dr. Spahn. "If we could learn why, we might gain valuable insight that could help us better treat all our asthma patients."
Dr. Spahn and his colleagues also found that children with severe asthma have deceptively good lung function. The amount of air a person can exhale in a second, known as forced expiratory volume in one second or FEV1, is one of the primary measures used to diagnose and categorize a patient's asthma. Patients are deemed to have severe asthma when their FEV1 is less than 60 percent of the average value for healthy people of their size and age.
The adults in Spahn's study had an average FEV1 that was 57 percent of the healthy average. Children in the study, however, averaged an FEV1 of 74 percent of the healthy average, with many exceeding 90 percent. Although other symptoms, such as medication use and history of asthma attacks, clearly put them in the severe category, the FEV1 results alone would have indicated that more than 40 percent had mild asthma and only 28 percent severe disease.
"The good news is that children have significantly less impaired lung function than do adults with asthma," said Dr. Spahn. "The bad news is that existing guidelines do not reflect this fact, and physicians may be mistakenly reassured by normal or near normal lung function readings in their pediatric patients. As a result, they may fail to appreciate the severity of their patients' asthma and undertreat them."
The study also indicates that patients whose asthma began in childhood rapidly lose lung function through adolescence then level off to a more moderate decline as they reach adulthood. Patients whose asthma began in adulthood, however, lose lung function almost immediately.
"Child-onset and adult-onset asthma may be two distinct forms of the disease, one that is slowly progressive over time and another that is associated with significant loss of lung function very shortly after onset," said Dr. Spahn.
Source: National Jewish Research and Medical Center.