Effect of Comorbidities on Outcomes of Neurorehabilitation Interventions in Multiple Sclerosis

Background: Interest in comorbidities has increased in the past few years, but the effect of comorbidities on outcomes of multiple sclerosis (MS) neurorehabilitation interventions is unclear. The aim of this review was to identify and summarize the existing evidence regarding the effect of comorbidities on outcomes of neurorehabilitation interventions targeting people with MS. Methods: Five databases (Embase, MEDLINE through Ovid, PubMed Central, Cumulative Index to Nursing and Allied Health Literature, and Web of Science) were searched using index terms and keywords relating to MS and a wide range of rehabilitation interventions. Studies screened were limited to English-language randomized controlled trials. Information related to included and excluded comorbidities and how they were reported and described was extracted from the included studies. Results: Fifty-four neurorehabilitation randomized controlled trials were included and were grouped into categories: robotics/technology-enhanced (n = 7), task-oriented training/neurorehabilitation principles (n = 7), electrical stimulation (n = 12), temperature regulation (n = 6), magnetic field therapy (n = 5), vibration (n = 9), and miscellaneous (n = 8). Although the issue of comorbidity was considered in 40 studies, it was limited to excluding individuals from participating in the trials. Only two studies reported on comorbidity, but neither examined the possible mediating or moderating effect of comorbidities on intervention outcomes. Conclusions: This review documents important knowledge gaps about the effect of comorbidity on neurorehabilitation outcomes and identifies a critical need for future studies to address this issue. Without this information, we limit our understanding of the mechanisms of comorbidity and its effects on relevant clinical and research outcomes specific to neurorehabilitation.