Components of airway disease

To the Editors:

“What we think we know already often prevents us from learning” (Claude Bernard)

I endorse the view of Hargreave and Parameswaran 1 that the components of airway disease, inflammation (bronchitis), reversibility (asthma), and chronic airflow limitation (chronic obstructive pulmonary disease (COPD)), are not “mutually exclusive and […] commonly occur together.” I would like to mention further evidence in support of their position.

I would add the longitudinal (natural history) perspectives of the primary-care practitioner 2 and the epidemiologist 3. Clinical reports from primary care document that acute bronchitis can precede asthma, which then develops into severe COPD over a few years 4 to decades 2. Perhaps the best longitudinal evidence derives from a cluster-randomised, population-based 20-yr prospective study finding that asthma was the strongest risk factor for subsequent COPD, both in relative (hazard ratio (HR) = 12.5) and absolute (attributable risk (AR) = 18.5%) terms compared with tobacco smoking (HR = 2.9 for current smoking, AR = 6.7% for ever-smoking) 3.

The dogma that asthma and COPD are different diseases (and therefore should be studied separately) appears to have been derived from the mainly cross-sectional perspectives of academic referral lung specialists (adult and paediatric allergists, pulmonologists) who for the most part have not had the opportunity to observe the natural history of lung disease over a patient's lifetime. I can think of no better explanation for a recent statement by a prominent leader in lung research: “Chronic obstructive pulmonary disease is probably the only chronic disease for which the finger of blame can be pointed at a single risk factor – tobacco smoking” 5.