Patients with mild-to-moderate asthma may develop clinically significant chronic obstructive pulmonary disease

Little is known about the aetiology and clinical characteristics of COPD among people who have never smoked.

A case-control study was conducted to describe the potential risk factors for clinically significant COPD among smokers and people who had never smoked. Medical record reviews and scoring of high-resolution computed tomography (HRCT) findings were performed in patients with clinically significant COPD (defined as having post-bronchodilator FEV(1)/FVC < 0.7 and FEV(1) < 60% of the predicted values). Pathological analyses were performed in some patients following autopsy.

Among the 9493 subjects screened, 424 (4.5%) were diagnosed with clinically significant COPD. Forty-nine (11.6% of clinically significant COPD) were never smokers (NSCOPD), and a comparative group of 98 smoking patients with COPD was randomly selected (SMCOPD). NSCOPD was characterized by predominantly female sex (87.8%) and a high prevalence of physician-diagnosed asthma (61.2%). Similar levels of reduction in %FEV(1) and %FEF(25-75%) were found in NSCOPD and SMCOPD, but there were higher %DL(CO) values and fewer low attenuation areas on HRCT in NSCOPD. More than half of the NSCOPD patients without a history of asthma had features of asthma. More than one-third of NSCOPD patients with an asthma history had never had a severe attack. At autopsy, both NSCOPD and SMCOPD showed wall thickening and inflammatory cell infiltration in small airways, and the number of CD4(+)-T cells was increased in NSCOPD.

In elderly Japanese, COPD among never smokers is largely attributable to asthma. Airflow limitation in NSCOPD results from small airway disease (airway predominant phenotype) rather than parenchymal destruction (emphysematous phenotype).