Comorbidity in traumatic brain injury and functional outcomes: a systematic review

INTRODUCTION: Comorbidities in people with traumatic brain injury (TBI) may negatively impact injury recovery course and result in long-term disability. Despite the high prevalence of several categories of comorbidities in TBI, little is known about their association with patients' functional outcomes. We aimed to systematically review the current evidence to identify comorbidities that affect functional outcomes in adults with TBI. EVIDENCE ACQUISITION: A systematic search of Medline, Cochrane Central Register of Controlled Trials, Embase and PsycINFO was conducted from 1997 to 2020 for prospective and retrospective longitudinal studies published in English. Three researchers independently screened and assessed articles for fulfillment of the inclusion criteria. Quality assessment followed the Quality in Prognosis Studies tool and the Scottish Intercollegiate Guidelines Network methodology recommendations. EVIDENCE SYNTHESIS: Twenty-two studies of moderate quality discussed effects of comorbidities on functional outcomes of patients with TBI. Cognitive and physical functioning were negatively affected by comorbidities, although the strength of association, even within the same categories of comorbidity and functional outcome, differed from study to study. Severity of TBI, sex/gender, and age were important factors in the relationship. Due to methodological heterogeneity between studies, meta-analyses were not performed. CONCLUSIONS: Emerging evidence highlights the adverse effect of comorbidities on functional outcome in patients with TBI, so clinical attention to this topic is timely. Future research on the topic should emphasize time of comorbidity onset in relation to the TBI event, to support prevention, treatment, and rehabilitation. PROSPERO registration (CRD 42017070033).