Asthma: An Inflammatory Process

Asthma is defined as a chronic inflammatory disorder of the airways characterized by1

  • Variable and recurring respiratory symptoms
  • Airflow limitation or obstruction
  • Bronchial hyperresponsiveness

Right symptoms, wrong diagnosis

Many diseases present with symptoms similar to those seen in asthma.2,3 Understanding whether airway inflammation is present can help rule out these conditions and support a diagnosis of asthma.

Examples of conditions with symptoms similar to those seen in asthma:

  • Chronic cough
  • Gastroesophageal reflux disease (GERD)
  • Vocal cord dysfunction
  • Bronchitis
  • Chronic obstructive pulmonary disease (COPD)

Nitric oxide and allergic airway inflammation

During inflammation, higher-than-normal levels of nitric oxide (NO) are released from epithelial cells of the bronchial wall.4 The concentration of NO in exhaled breath, or fractional exhaled nitric oxide (FeNO), can help identify airway inflammation, and thereby support a diagnosis of asthma when other objective evidence is lacking.5

 

Measuring FeNO

Traditional methods of asthma assessment only give part of the picture, as they are only indirectly associated with airway inflammation.5

In addition, conventional evaluation methods such as peak flow measurement and spirometry are effort dependent, and results may be unreliable. Likewise, symptom assessments are subjective and lack sensitivity.6

FeNO adds a new dimension to traditional clinical tools

The American Thoracic Society (ATS) strongly recommends the use of FeNO measurement to aid in the assessment, management, and long-term monitoring of asthma.5 In their 2011 clinical practice guideline, the ATS emphasizes the importance of using FeNO to

  • Understand possible causes of respiratory symptoms where there is no diagnosis of asthma
  • Ensure appropriate treatment with anti-inflammatory medications, especially corticosteroids
    • Patients with asthma caused by allergic airway inflammation have high levels of FeNO that decrease with corticosteroid treatment
    • Knowing whether airway inflammation is present can help avoid an empiric trial of steroids

References: 1. National Asthma Education and Prevention Program; National Heart, Lung, and Blood Institute. Expert panel report 3: guidelines for the diagnosis and management of asthma. Full report 2007. http://www.nhlbi.nih.gov/guidelines/asthma/asthgdln.pdf. Published August 28, 2007. Accessed September 13, 2011. 2. Morice AH, Fontana GA, Sovijarvi ARA, et al; on behalf of the ERS Task Force. The diagnosis and management of chronic cough. Eur Respir J. 2004;24:481-492. 3. Tilles SA. Differential diagnosis of adult asthma. Med Clin N Am. 2006;90:61-76. 4. Van Den Toorn LM, Overbeek SE, De Jongste JC, Leman K, Hoogsteden HC, Prins J-B. Airway inflammation is present during clinical remission of atopic asthma. Am J Respir Crit Care Med. 2001;164:2107-2113. 5. Dweik RA, Boggs PB, Erzurum SC, et al; on behalf of the American Thoracic Society Committee on Interpretation of Exhaled Nitric Oxide Levels (FeNO) for Clinical Applications. An official ATS clinical practice guideline: interpretation of exhaled nitric oxide levels (FeNO) for clinical applications. Am J Respir Crit Care Med. 2011;184:602-615. 6. Smith AD, Cowan JO, Filsell S, et al. Diagnosing asthma: comparisons between exhaled nitric oxide measurements and conventional tests. Am J Respir Crit Care Med. 2004;169:473-478. 7. Knuffman JE, Sorkness CA, Lemanske RF Jr, et al; for the Childhood Asthma Research and Education Network of the National Heart, Lung, and Blood Institute. Phenotypic predictors of long-term response to inhaled corticosteroid and leukotriene modifier therapies in pediatric asthma. J Allergy Clin Immunol. 2009;123:411-416. 8. Szefler SJ, Martin RJ, King TS, et al; for the Asthma Clinical Research Network of the National Heart, Lung, and Blood Institute. Significant variability in response to inhaled corticosteroids for persistent asthma. J Allergy Clin Immunol. 2002;109:410-418. 9. Smith AD, Cowen JO, Brassett KP, et al. Exhaled nitric oxide: a predictor of steroid response. Am J Respir Crit Care Med. 2005;172:453-459.

FeNO predicts the likelihood of steroid responsiveness more consistently than spirometry, bronchodilator response, peak flow variation, or airway hyperresponsiveness to methacholine.7-9

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