Revealing Methodological Challenges in Chronic Obstructive Pulmonary Disease Studies Assessing Comorbidities: A Narrative Review

Beyond respiratory impairment, patients with chronic obstructive pulmonary disease (COPD) often suffer from comorbidities which are associated with worse health status, higher health care costs and worse prognosis. Reported prevalences of comorbidities largely differ between studies which might be explained by different assessment methods (objective assessment, self-reported assessment, or assessment by medical records), heterogeneous study populations, inappropriate control groups, incomparable methodologies, etc. This narrative review demonstrates and further evaluates the variability in prevalence of several comorbidities in patients with COPD and control individuals and discusses several shortcomings and pitfalls which need to be considered when interpreting comorbidity data. Like in other chronic organ diseases, the accurate diagnosis and integrated management of comorbidities is a key for outcome in COPD. This review highlights that there is a need to move from the starting point of an established index disease towards the concept of the development of multimorbidity in the elderly including COPD as an important and highly prevalent pulmonary component.