Prevalence, Burden, Epidemiology, and Pathophysiology of Asthma

James F. Donohue, MD

The prevalence and cost of asthma are considerable. In 2010, an estimated 25.7 million Americans had asthma, and direct and indirect costs related to the care of this disorder totaled a staggering $56 billion in 2007.^1,2 According to the 2012 Behavioral Risk Factor Surveillance System, 49% of patients with asthma reported an attack in the past year, 11% reported no symptoms in the past year, and 43% reported no physician visits in the past year. Furthermore, only 27% of patients reported having an asthma management plan, and 33% reported missing work or days of reduced activity.³ Clearly, there is room for improvement when it comes to the management of asthma in the United States. One of the most important questions facing practitioners when a patient presents with symptoms of cough, wheezing, nocturnal signs, and sleep disruption, is whether the individual has asthma.⁴ To establish a diagnosis, practitioners should access patient history, and inquire about symptoms to determine if they are consistent with recurrent episodes of airflow obstruction.⁴ The key signs of asthma include recurrent wheezing, shortness of breath, chest tightness, and cough that vary over time and intensity.⁴ Variable expiratory airflow limitation is noted if measurements of peak expiratory flow rates are made. Typically, symptoms are worse at night or in the early morning, and may be triggered by infections, exercise, allergens, weather, and irritants.⁴ Obesity is an important risk factor for asthma, as it often results in an altered pulmonary physiology and increased airway resistance. In addition, obesity is associated with more asthma exacerbations, especially in women.⁵ Patients with asthma who are obese tend to have more airway symptoms and airway inflammation. These patients also respond differently to asthma medications. Therefore, it is imperative to manage obesity in order to improve airway hyperresponsiveness and inflammation.^6-8 Various tools can be used to assess and monitor asthma, such as spirometry, which provides an objective measure of lung function; the forced expiratory volume in 1 second (FEV1)/forced vital capacity ratio of >0.75 to 0.80 is considered normal in adult patients.³ Other asthma assessment tools include asthma control questionnaires, asthma control tests, and peak flow meters.⁹ The clinical symptoms of asthma may vary greatly in terms of severity. Some of the characteristics of severe asthma include chronic airflow obstruction, eosinophilic and/or neutrophilic asthma, corticosteroid insensitivity, and recurrent exacerbations.⁹ Given the fact that asthma is heterogenous in terms of the underlying clinical and inflammatory phenotypes involved, the care of patients is moving toward a more personalized, targeted approach. In the future, we will have phenotype-targeted treatments based on the pathophysiology and biomarkers of asthma.¹⁰ Phenotyping patients with asthma with links to pathophysiological mechanisms will lead to a more precise, rational way of providing specific treatments to the individual patient. For example, patients with recurrent exacerbations who have sputum or blood eosinophils may be candidates for anti-interleukin-5 antibody treatment; and patients with chronic airflow obstruction, airway wall remodeling, low FEV1 levels, and high serum periostin levels may be candidates for antiinterleukin-13 antibody treatment. In addition, patients with neutrophils in the sputum may be more responsive to macrolide antibiotics, and patients with eosinophilic asthma may be more responsive to an anti-interleukin-4 receptor.¹⁰

References

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2. Barnett SB, Nurmagambetov TA. Costs of asthma in the United States: 2002-2007. J Allergy Clin Immunol. 2011;127:145-152.
3. Centers for Disease Control and Prevention. 2012 BRFSS asthma call-back survey prevalence tables. www.scdhec.gov/Health/DiseasesandConditions/Asthma/AsthmaFacts/. Accessed November 21, 2014.
4. Global Institute for Asthma. Global strategy for asthma management and prevention. Revised 2014. www.ginasthma.org/local/uploads/files/GINA. Accessed November 21, 2014.
5. Heacock T, Lugogo N. Role of weight management in asthma symptoms and control. Immunol Allergy Clin North Am. 2014;34:797-808.
6. Scott HA, Gibson PG, Garg ML, et al. Dietary restriction and exercise improve airway inflammation and clinical outcomes in overweight and obese asthma: a randomized trial. Clin Exp Allergy. 2013;43:36-49.
7. Dogra S, Kuk JL, Baker J, Jamnik V. Exercise is associated with improved asthma control in adults. Eur Respir J. 2011;37:318-323.
8. Mendes FA, Almeida FM, Cukier A, et al. Effects of aerobic training on airway inflammation in asthmatic patients. Med Sci Sports Exerc. 2011;43:197-203.
9. National Heart, Lung, and Blood Institute. Expert Panel Report 3: Guidelines for the Diagnosis and Management of Asthma. www.nhlbi.nih.gov/files/docs/guidelines/asthgdln.pdf. Accessed November 21, 2014.
10. Chung KF. New treatments for severe treatment-resistant asthma: targeting the right patient. Lancet Respir Med. 2013;1:639-652.

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