Traumatic brain injury (TBI) is a leading cause of death and disability . Increasingly, mild (M)TBI (concussion) has been recognized as a public-health concern especially for teenagers and young adults  because it can potentially lead to significant disruptions in education and working life . It is estimated that MTBI represents 70% to 90% of all treated cases of TBI, and that the incidence of hospital treatment in adults with MTBI ranges from about 100 to 300 per 100,000 person-years . However, because a large number of MTBI cases are not treated in hospital, the incidence of all MTBI among adults is likely to be in excess of 600 per 100,000 person-years . The economic effect of MTBI is substantial, accounting for approximately 44% of the US$60 billion annual cost of TBI in the USA [4, 5]. It has been reported that most of these cases recover within 3 to 12 months; however, some studies suggest that a considerable minority continue to report distressing symptoms that persist . Patients often experience a combination of physical, emotional, and cognitive symptoms, collectively known as post-concussion syndrome (PCS) . Commonly reported PCS symptoms include headaches, balance problems, dizziness, fatigue, depression, anxiety, irritability, and memory and attention difficulties, which can have a considerable negative effect on the patient's ability to return to pre-injury function, work, and/or school . In addition, there is some evidence that MTBI is associated with an increased risk for certain neurological and/or psychiatric disorders, including Parkinson's disease (PD), early-onset dementia, chronic traumatic encephalopathy, and schizophrenia [7–11].
In its last review, the WHO Collaborating Centre for Neurotrauma, Prevention, Management and Rehabilitation Task Force found that studies addressing issues of prognosis had a low scientific quality . Specifically, the Task Force found a scarcity of good-quality studies on prognostic factors in both older people and children, and very few scientifically admissible studies on the health effects of multiple concussions . There were too few studies on the long-term consequences of MTBI following repeated head injuries, such as in hockey and/or American football, to make any strong conclusions . Additionally, the previous review identified only sparse evidence on interventions after MTBI . The presence of head injuries in military personnel is also an important concern, given the prevalence of blast-related war injuries sustained in areas such as Iraq and Afghanistan . In addition to these knowledge gaps, the Task Force did not find any acceptable studies on return to work or school after MTBI, nor did it find any studies that had developed prediction rules to identify those at risk for not recovering and/or developing longer-term health problems .
Prognosis is a central issue in health care, which is related to both the identification of individuals at risk for poor recovery, and identification of modifiable risk factors and feasible treatment strategies . From a diagnostic point of view, screening for those at risk for poor recovery could potentially help to triage patients into more effective health interventions. Additionally, any intervention can also be viewed as a modifiable prognostic factor, and to be a useful intervention, it must improve prognosis. Given that resources are limited, it is important to compare the effectiveness of interventions versus the modification of prognostic factors (for example, psychosocial factors) in reducing the burden of disease in both patients and society at large. In order to develop prediction rules to aid clinical decision-making, it is of the utmost importance that information on prognostic factors is available from scientifically valid studies. Given the numbers of people affected by MTBI, the ability to triage patients at risk for poor recovery to allow focused and cost-effective management strategies becomes an important health policy issue.
In this study, we proposed to update the WHO Collaborating Centre Task Force findings on prognosis in both the adult and pediatric populations to: 1) describe the course and identify prognostic factors of recovery after MTBI, for example, following work injuries, traffic injuries, sports injuries and military-related MTBI; 2) describe the long-term sequelae of MTBI (such as brain tumor, dementia, PD, Alzheimer's disease, chronic pain, chronic traumatic encephalopathy, attention deficit and hyperactivity disorder, and disability); 3) identify modifiable prognostic factors; 4) identify candidate prognostic factors to be used to develop clinical prediction rules for early identification of patients at risk for poor recovery after MTBI; 5) make clinical and methodological recommendations for future research to address prognosis after MTBI; and 6) evaluate the effectiveness of clinical interventions for the management of MTBI (for example, medical, rehabilitative, and/or vocational).