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Asthma: An Inflammatory Process

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

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

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:

  • A chronic cough
  • Gastroesophageal reflux disease (GERD)
  • Vocal cord dysfunction
  • Eosinophilic bronchitis
  • Chronic obstructive pulmonary disease (COPD)

Normal bronchiole

Normal bronchiole

Asthmatic bronchiole

Asthmatic bronchiole

Nitric oxide and Th2/type 2 allergic/eosinophilic driven airway inflammation

During airway 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 allergic/eosinophilic inflammation, and thereby support a diagnosis of asthma when other objective evidence is lacking.5

Normal epithelial cells release minimal NO

Normal epithelial cells release minimal NO

During airway inflammation, activated epithelial cells increase production of NO

During airway inflammation, activated epithelial cells increase production of NO

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.