Issues of comorbidity in clinical guidelines and systematic reviews from a rehabilitation perspective

BACKGROUND: Systematic reviews have a major role for evidence-based care and found the basis of clinical guidelines. In rehabilitation, typical patients have co- or even multimorbidities, present in different patterns. The primary aim of this paper is to raise different conceptual and methodological issues regarding the role of comorbidity and multimorbidity in systematic reviews. Specifically, we aim to examine how issues of comorbidity and multimorbidity are addressed in clinical guidelines and systematic reviews with a special emphasis on rehabilitation care. METHODS: We use systematic reviews of interventions in unspecific low back pain (LBP) as a case in point, because of its importance to rehabilitation care and its known comorbidities. We searched the Cochrane Library for systematic reviews on LBP and identified the different ways of handling issues of co-/multimorbidity within these reviews. We also searched for methodological studies related to co- and multimorbidities within guidelines. RESULTS: We identified 49 systematic reviews on LBP published between 2004 and 2017 and excluded 11 reviews for various reasons. In the remaining 38 reviews we found only scant evidence that comorbidities were considered. Comorbidities are entered in a systematic review, mostly on a superficial level, in terms of introducing LBP as a multifactorial disorder or disorders that are associated with LBP, as a target of an intervention, in the planning of the review in terms of planned subgroup analysis, as exclusion criteria within original studies or systematic reviews, as outcomes, and in the conclusion section as necessary target groups of the intervention (i.e. subgroups). CONCLUSIONS: There is a clear-cut need to address comorbidities both in systematic reviews and clinical guidelines. Systematic reviews should consider co-/multimorbidities in their exclusion/inclusion criteria, should extract data on comorbidities from the original studies, and address the topic of pre-specified subgroup analyses. However, the theoretical and empirical basis for the inclusion of comorbidities issues in systematic reviews has to be further developed both in epidemiological and clinical studies.