COPD patients who have emphysema and airway thickening on computed tomography findings have more hospitalizations and more severe dyspnea, according to the results of a study by Dr. Van Tho Nguyen and colleagues from the Shiga University of Medical Science, Otsu, Shiga, Japan, and the University Medical Center at Ho Chi Minh City, Vietnam.
Pulmonary function testing may not fully represent the heterogenous characteristics of COPD, according to the researchers, who used quantitative CT to develop a method to phenotype COPD and examine differences in clinical outcomes between mixed phenotype patients and those with emphysema- and airway-dominant phenotypes.
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The mixed phenotype was associated with more severe dyspnea and more frequent hospitalizations, and these patients may need more attention and interventions, the researchers said (Ann Am Thorac Soc Vol 12, No 7, pp 988–996, Jul 2015).
The researchers performed pulmonary function testing and whole-lung CT scans on 240 male smokers with COPD and 187 male smokers without COPD. Four phenotypical classifications were defined on the basis of measurements of airway thickening and percentage of low-attenuation volume (threshold of -950 Hounsfield units) – CT-normal, airway-dominant, emphysema-dominant, and mixed phenotype.
Of the 240 patients with COPD, 43% had the emphysema-dominant phenotype, 22% had the CT-normal phenotype, 19% had a mixed phenotype, and 16% had the airway-dominant phenotype.
Patients with mixed phenotype COPD were found to have more severe air trapping (residual volume/total lung capacity, RV/TLC) and airflow limitation (FEV1/FVC and FEV1% predicted) compared to the other phenotypes. Likewise, mixed phenotype COPD patients had lower percent predicted carbon monoxide diffusing capacity than the airway-dominant phenotype (P<0.0001) and the CT-normal phenotype (P<0.0001).
Furthermore, patients with mixed phenotype COPD had 2.0 to 3.6 more hospitalizations for COPD exacerbations (P<0.05) and more severe dyspnea (P<0.01) than the other CT-based COPD phenotypes. The differences persisted after adjusting for BMI, FEV1, age, smoking status, and pack-years.
Further, the mixed COPD phenotype was associated with a longer duration of disease and a higher blood neutrophil count, which has been linked to higher risk of recurrent exacerbations and may lead to emphysema progression.
The researchers theorize that these patients have more severe dyspnea and therefore are diagnosed earlier or it may take longer for both airway thickening and emphysema to develop.
Dr. Nakano and Ogawa reported receiving grants from the Japan Society for the Promotion of Science and Dr. Nakano reported receiving fees from GSK and Nippon Boehringer Ingelheim.
Quantitative CT can be used to classify COPD patients as having either airway-dominant, emphysema-dominant, or mixed-phenotype based on the severity of airway thickening versus emphysema. Frequent exacerbations and cough is found in the airway-dominant COPD phenotype, whereas, the emphysema-dominant phenotype have more severe dyspnea, lower BMI, rapid loss of FEV-1, and higher respiratory associated mortality.