The importance of symptoms in the longitudinal variability of clusters in COPD patients: A validation study

Cluster analysis has been utilized to explore phenotypic heterogeneity in chronic obstructive pulmonary disease (COPD). To date, little is known about the longitudinal variability of clusters in COPD patients. We aimed to evaluate the 2-year cluster variability in stable COPD patients.

We evaluated the following variables in COPD patients at baseline and 2 years later: age, gender, pack-year history, body mass index (BMI), modified Medical Research Council (MMRC) scale, 6-min walking distance (6MWD), spirometry and COPD Assessment Test (CAT). Patient classification was performed using cluster analysis at baseline and 2 years later. Each patient's cluster variability after 2 years and its parameters associated with cluster change were explored.

A total of 521 smokers with COPD were evaluated at baseline and 2 years later. Three different clusters were consistently identified at both evaluation times: cluster A (of younger age, mild airway limitation, few symptoms), cluster B (intermediate) and cluster C (of older age, severe airway limitation and highly symptomatic). Two years later, 70% of patients were unchanged, whereas 30% changed from one cluster to another: 20% from A to B; 15% from B to A; 15% from B to C; 42% from C to B and 8% from C to A. 6MWD, forced expiratory volume in 1 s (FEV₁ ) % and CAT were the principal parameters responsible for this change.

After 2 years of follow-up, most of the COPD patients maintained their cluster assignment. Exercise tolerance, lung function and quality of life were the main driving parameters in those who change their cluster assignment.