Background and objective: Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease often viewed as part of a multimorbidity complex. There is a need for better phenotyping of the disease, characterization of its interplay with other comorbidities and its association with long-term outcomes. This study aims to examine how clusters of comorbidities are associated with severe exacerbations and mortality in COPD.

Methods: Participants with potential COPD were recruited from the second (1995-1997) and third (2006-2008) survey of the HUNT Study and followed up until April 2020. Ten objectively identified comorbidities were clustered using self-organizing maps. Severe COPD exacerbations requiring hospitalization were assessed using hospital data. All-cause mortality was collected from national registries. Multivariable Cox regression was used to calculate hazard ratios (HRs) with 95% CIs for the association between comorbidity clusters and all-cause mortality. Poisson regression was used to calculate incidence rate ratios (IRRs) with 95% CI for the cumulative number of severe exacerbations for each cluster.

Results: Five distinct clusters were identified, including 'less comorbidity', 'psychological', 'cardiovascular', 'metabolic' and 'cachectic' clusters. Using the less comorbidity cluster as reference, the psychological and cachectic clusters were associated with all-cause mortality (HR 1.23 [1.04-1.45] and HR 1.83 [1.52-2.20], adjusted for age and sex). The same clusters also had increased risk of exacerbations (unadjusted IRR of 1.24 [95% CI 1.04-1.48] and 1.50 [95% CI 1.23-1.83], respectively).

Conclusion: During 25 years of follow-up, individuals in the psychological and cachectic clusters had increased mortality. Furthermore, these clusters were associated with increased risk of severe COPD exacerbations.