diseases. Prevalence and incidence density of comorbidity was also calculated for disease clusters. Highest prevalence rates at the time of the diabetes diagnosis were reported for cardiovascular diseases (64%) and musculoskeletal diseases (31%). This study showed that the diabetes patient population is heterogeneous in terms of comorbidity, and that the diabetes patient without (discordant) comorbidity is relatively rare. Consequently, the relative ignorance of (discordant) comorbidity in evidence-based diabetes guidelines is inappropriate. Guidelines should better explicit how comorbidity may interfere with diabetes management, which may be the case for discordant comorbidity especially, and should adjust recommendations accordingly.
In the same primary care cohort of patients with type 2 diabetes, Chapter 3 explored the associations between longitudinal diabetes control parameters and the number and specific types of chronic comorbidity. A mixed model analysis technique was applied to compare longitudinal trends of HbA1c and systolic blood pressure (SBP) during five years of follow-up between groups of diabetes patients with different comorbidity profiles. The simple sum of comorbid diseases did not show an unfavourable association with diabetes control parameter trends over five years, but specific types of comorbidity did. Diabetes patients with comorbid musculoskeletal disease had statistically significantly higher HbA1c values after five years, with lower values around the diabetes diagnosis, compared to patients without comorbid musculoskeletal disease. Diabetes patients with comorbid cardiovascular disease had significantly sustained elevated values of SBP from the diabetes diagnosis onwards, compared to diabetes patients without comorbid cardiovascular disease. The number of comorbid diseases was significantly associated with the five year trend of SBP (not that of HbA1c), with highest values after five years for diabetes patients without comorbidity, and effect modification by socioeconomic status. Causal relations cannot be inferred from the explorative, observational design of this study. It was hypothesised that the reduced ability for physical exercising could explain the increasing HbA1c values over five years among the patients with comorbid musculoskeletal disease, and that the concordance of the cardiovascular comorbidity explained the results among this comorbidity group on the longitudinal SBP outcomes. The observation that not just the sum of diseases negatively influenced the course of diabetes control parameters, but that this did occur under presence of specific types of comorbidity, emphasised that the diabetes care provided by GPs is part of general healthcare delivered to ‘whole persons’, i.e. ‘person-centred care’. Apparently, the patient-specific context intervened. GPs integrated disease-
CHAPTER 8
contribute to the development of personalised diabetes management by formulating different therapeutic approaches that are appropriate for diabetes patients with a specific comorbidity burden.
In Chapter 4, associations between comorbid COPD and longitudinal diabetes control parameters over five years of follow-up were explored in the type 2 diabetes patients cohort. Trends in HbA1c and SBP were compared with mixed model analyses between patients with and without comorbid COPD. Subgroup effect analyses explored potential effect modification of these trends (according to presence or absence of COPD) by age, sex, body mass index, and socioeconomic status. It showed that diabetes patients with comorbid COPD have different trends of SBP over five years compared to diabetes patients without COPD, an effect that was modified by socioeconomic status and body mass index. In contrast to diabetes patients without COPD, in whom an increasing body mass index is associated with increasing SBP levels, the trend of SBP in diabetes patients with comorbid COPD is defined more by the socioeconomic status than by the body mass index. Type 2 diabetes and COPD, both common chronic diseases with substantial combined occurrence, interfere with one another. Ongoing research is needed to further disentangle the complex associations between comorbidity of diabetes, COPD, diabetes control parameters, and the other patient characteristics; and to define how this translates into practical recommendations. It is clear however that the interference of these two common chronic diseases deserves attention from healthcare professionals taking care of patients with either disease, and that comorbidity needs to be recognised as a patient characteristic with possible influence on disease-specific outcomes of an index-disease. The second part of this thesis contained qualitative research. A focus group study was performed with a purposive sample of Dutch GPs to ensure heterogeneity in characteristics such as age, sex, and urbanisation among the participants. Exploration of their considerations and main objectives in the management of multimorbidity, and factors influencing this management was the first aim. Second aim was to explore how GPs value guidelines when applied to patients with multimorbidity, and which benefits and barriers they experience from adherence to guidelines in these patients. In the iterative qualitative process, in which data collection and analysis alternate, the insight grew that discussions on the role of guidelines, applied to patients with multimorbidity, provided important information meriting deeper exploration on itself. This resulted in formulating the second, separate research question. The focus groups were guided by an experienced moderator, who used an interview guide. Interviews were transcribed verbatim. Data collection proceeded until saturation was reached. Data analysis was performed by two researchers using the constant comparison analysis technique.