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Thursday, August 28, 2014

Airway remodeling discovered in mild intermittent asthma

A problem the sometimes results in patients with asthma is airway changes, or remodeling, that become permanent.  The end result here is thickening of the airway walls resulting in irreversible air-flow obstruction.

What would cause airway remodeling in asthmatics:
  1. Mucosal infiltration by inflammatory cells
  2. Deposition of connective tissue on the extracellular matric
  3. Increase in muscle mass, mucus glands, and vessel area
Such remodeling not only occurs in central airways but in peripheral airways as well.  

What are the pathological features of airway remodeling in asthma? 
  1. Hypertrophy of mucus-secreting glands
  2. Subepithelial fibrosis
  3. Marked thickening of basement membrany
  4. Hyperplasia
  5. Hypertrophy of airway smooth muscle
However, the reversible components of asthma will still exist, such as edema, infiltration by inflammatory cells, and bronchoconstriction.  They can be treated by inhaled corticosteroids and bronchodilators. 

What is the result of airway remodeling in asthmatics?
  1. Some degree of irreversible air-flow obstruction, that results in mild shortness of breath all the time that is not reversed with albuterol
  2. Increased risk that the airways will respond to asthma triggers, or an increased risk that an asthma attack will occur
  3. Increased in the number of medicines required to treat asthma
  4. Higher doses of medicine, meaning greater risk for side effects
  5. Greater risk for hospitalizations
  6. Increased cost of caring for such asthmatics.  
Studies show that airway remodeling and thickened airways may occur even in asthmatics with mild intermittent asthma, and that patients with asthma have thicker airway walls than patients without asthma.  Likewise, asthmatics with severe asthma have thicker airways than subjects with milder disease.

Essentially, airway remodeling is the result of chronic inflammation in the airways that goes untreated long-term.  This is added evidence that asthma should be treated aggressively with inhaled corticosteroids early on in the course of the disease to prevent permanent airway damage and worsening asthma.

Researchers also believe that a good non-invasive tool for measuring for airway thickness and remodeling is high resolution computed tomography, or high resolution cat scan (a CT). 

  1. Asker, Aelvi, et al, "Evaluation of Airway Wall Thickness Via High-Resolution Computed Tomograhy in Mild Intermittent Asthma," Respiratory Care, April, 2014, volume 59, number 4, pages 550-555
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