Multiple conditions and clinical trials: A systematic review of the impact of multimorbidity in inclusion, assessment and outcome of self-management studies.

The problem

Multimorbidity has many potential implications for health care delivery, but a particularly important impact of multimorbidity concerns the validity of trial evidence underpinning clinical guidelines for individual conditions. There has been no detailed analysis of the impact of multimorbidity in self-management trials. The current study explores how authors of published trials of self-management interventions have managed inclusion, description and impact of multimorbidity in exemplar disorders. The aim was to assess current approaches to the management of multimorbidity in the context of trials, and to consider implications for evidence synthesis and reporting.

The approach

To achieve our aims, we restricted our analysis to a small number of exemplar conditions, where multimorbidity is common and where there is a known self-management literature: type II diabetes; coronary heart disease (CHD) and chronic obstructive pulmonary disease (COPD). We focussed our search on published Cochrane reviews. Data were extracted from the trials on inclusion/exclusion (proportion of studies excluding patients with multimorbidity at baseline); description (reporting of sample characteristics in terms of multimorbidity); and outcomes (analyses of the impact of multimorbidity on outcomes through secondary and moderating analyses).

Findings

Eleven reviews identifying 164 unique trials were identified. Inclusion/exclusion: across conditions, 55% of trials reported excluding patients with forms of multimorbidity. Reasons for exclusion were poorly described or defined and the number of studies excluding based on multimorbidity varied across conditions. Description: reporting of multimorbidity within the trials was poor, with only 35% of trials reporting on multimorbidity in their patient samples. Those that did report other conditions only reported on a small number of comorbid conditions such as hypertension and heart disease.

Outcomes

secondary analyses exploring the impact of multimorbidity was very rare. Three trials (1.8%) reported analysis of moderation by multimorbidity, 4 trials reported on impact of the intervention on comorbid depression/ anxiety, and 2 trials used multimorbidity in the analysis as a covariate.

Consequences

The number of patients with multimorbidity is increasing and patients with one initial long-term condition are likely to develop further conditions. Regardless, intervention trials continue to be disease specific even though many conditions may benefit from similar interventions (ie education, diet and exercise). Trials often exclude patients with multimorbidity, and reporting of multimorbidity in trials including such patients is generally poor. This limits judgements of the external validity of the results for clinical populations. A consistent approach to the conduct and reporting of secondary analyses of the effects of multimorbidity on outcomes, using current best practice guidance, could lead to a rapid development of the evidence base.