A Study Challenges the Validity of Classifying Chronic Obstructive Pulmonary Disease into Defined Subgroups

A large study with multiple cohorts reveals that the classification of Chronic Obstructive Pulmonary Disease (COPD) into mutually exclusive subgroups is poorly reproducible across different cohorts, and that COPD is better characterized by continuous traits that can coexist to varying degrees within the same person.  The study, led by ISGlobal, an institution supported by the “la Caixa” Foundation, was published in Thorax. The results have implications for COPD research and clinical management.

Chronic obstructive pulmonary disease is a highly heterogeneous disease and there is little consensus on the existence and definition of different subtypes of COPD. Several groups have used cluster analysis to identify disease subtypes (i.e. algorithms to group cases into more homogenous groups, based on clinical parameters). However, the reproducibility of this classification has been relatively low, calling into question the use of this type of research for the clinical management of the disease in the short-term.  

The aim of this study, the largest performed to date, was to determine whether the COPD subtypes identified by clustering algorithms are reproducible in different patient populations. More than 1,700 persons with COPD were analysed using the same algorithm and the same COPD-related characteristics across cohorts. The results show that the reproducibility of COPD classification into subtypes (e.g. very severe phenotype or cardiovascular phenotype) was moderate to low. In contrast, relationships between individual clinical manifestations (such as pulmonary function or cardiovascular comorbidity) were more consistent. These manifestations respond to a continuous spectrum of disease severity and can coexist to varying degrees within the same patient. 

“This means that COPD phenotypical heterogeneity is better explained if one considers the individual traits rather than trying to classify the patients in well-defined groups” explains Judith Garcia-Aymerich, study coordinator.  “Our results challenge the idea that individual studies that classify the disease in defined subtypes may be immediately interpreted in terms of different causes and treatments for each subgroup”, she adds.   

Reference:

Castaldi PJ, Benet M, Petersen H, et al. Do COPD subtypes really exist? COPD heterogeneity and clustering in 10 independent cohorts. Thorax. 2017 Jun 21. doi: 10.1136/thoraxjnl-2016-209846.