Introduction
Traumatic Brain Injury (TBI) is worldwide known as a major public health concern potentially resulting in death or neurological impairment [
1,
2]. The incidence of TBI is about 300 per 100,000 inhabitants [
3] with almost 50% related to traffic accidents in the Western civilization [
4].
Due to increasing clinical experience and improved treatment algorithms, overall mortality decreased during the last thirty years in traumatized patients [
5]. Thus, research also focused on long-term outcome after major trauma including TBI. However, despite this increasing interest in research on long-term outcome following trauma in general, patients with TBI were frequently omitted from study populations due to the known impact on mortality [
6]. Furthermore, many long-term outcome studies including patients with TBI exhibit potential limitations. First, research emphasizing on multiple trauma patients might not estimate the complexity of the impact of TBI as the presence of multiple injuries influences morbidity and long-term perceptions [
5,
7]. The same limitation might be observed in studies emphasizing TBI without excluding other severe injuries resulting in compromised comparisons between isolated and multiple traumatized patients of different injury severity [
6,
8]. In conclusion, only limited information on long term recovery and morbidity more than 10 years after isolated TBI are available [
3,
9‐
11]. Furthermore, these reports commonly focused only on the impact of mild TBI [
3,
9], moderate or severe TBI [
10] or special subgroups [
11] limiting general assumptions. Consequently, more comprehensive long-term outcome studies after isolated TBI are required in order to document potential prognosis and to prepare life plans for survivors, families and clinicians [
10]. In the presented study we aimed to verify medical, social as well as vocational long-term outcome results after mild, moderate and severe TBI in one of the largest long-term outcome study populations after isolated TBI in Europe.
Discussion
The current paper presents first results of one of the largest long-term outcome studies after isolated TBI in Europe. With the intention to verify medical, social as well as vocational long-term deficits following TBI in survivors our results can be summarized as follows:
Patients with severe TBI were significantly younger and more often of male gender than those with moderate or mild TBI. The analysis of living conditions revealed more individuals living alone in the severe TBI population after trauma compared to the other TBI groups. A significantly worse outcome according to the GOS as well as a higher incidence of mental disabilities was found after severe TBI. Patients with severe TBI were more often confined to bed than patients after moderate or mild TBI. Severe TBI significantly impacts vocational situation due to an occupational decline resulting in loss of regular income. Moderate and severe TBI were not associated with increased unemployment or professional retraining compared to patients with mild TBI.
Outcome after TBI has been investigated in different settings [
3,
9‐
11,
16,
17]. However, knowledge of the influence of isolated TBI on long-term outcome remains sparse due to several reasons. First, the studies varied considerably according to the definition of “long-term” with a posttraumatic observation period between 5 and 15 years [
9,
16,
17]. Furthermore, some studies focused either only on the impact of mild TBI [
3,
9] or on the combination of moderate and severe TBI [
10,
16], whereas others verified outcome results only in multiple traumatized patients [
5,
7]. Third, due to the high mortality after severe TBI even 10 years after trauma [
1] and the reduced probability of severe isolated head injuries after high energy trauma [
4,
22], included study populations used to be relatively small.
In the presented study we were obviously faced with the same problem: Almost 50% of the overall study population had to be excluded initially mainly because of in-hospital mortality or the presence of major concomitant injuries. The inclusion rate of 14.1% in our study is in line with current literature. For instance, Cameron et al. analyzed the 10-year outcome after TBI excluding not explicitly further injuries [
6]. Identifying an overall potential population of 21,032 patients based upon a Canadian state registry, finally 1,290 took part in the re-examination (6.1%) [
6]. In addition, Andersson and colleagues analyzed 198 patients evaluated from a main population of 1,719 patients with mild TBI (11.5%) [
9].
According to the demonstrated demographic results, patients suffering severe TBI were significantly younger and more often of male gender compared to those with moderate or mild TBI. This over-representation of young and male trauma victims has been elucidated in isolated TBI as well as in multiple trauma patients previously [
6,
8,
10]. One explanation for the increased incidence of severe injuries in these patients might be argued by the relatively high frequency of traffic accidents [
4] as especially young male patients are known to be involved in high energy trauma [
4]. In this context, road traffic accidents have been found responsible for up to 80% of TBI patients [
4].
The living situation after isolated TBI is suspected to be a critical factor for quality of life and daily living activities. Living alone may be a sign of social isolation, but it may also reflect independence [
10,
16]. Nevertheless, it seems unlikely to expect that patients surviving severe TBI would be more capable of independent living than those with minor head injuries [
10]. In this context, we found more “singles” and divorced individuals after severe TBI compared to moderate or mild TBI. Therefore, the prevalence of living alone presumably reflects social isolation. This suggestion has been also considered by Colantonio et al., who found individuals living alone in up to 60% after moderate to severe TBI [
10]. In addition, even after isolated mild TBI an increased incidence of separated relationships has been found: Moreover, the measured incidence of 7% divorced patients meets the presented results (8.3%) [
9]. However, as children were also included in the present study, many participants could still be living with their parents. This may be an indicator of more supportive environment but also could indicate compromised independence [
8,
10]. The latter aspect is strongly supported by the measured incidence of patients who were confined to bed due to TBI sequelae and those stating an inability to manage common homework in the presented study.
Focusing on long-term outcome measurements, the presented data indicates that survivors of severe TBI had significant impairments: These patients achieved significantly reduced GOS-scores accompanied with increased incidence of mental disability. These findings are congruent with the current literature. Colantonio et al. compared mental tests of patients after moderate to severe TBI with normative expected results revealing increased mental disabilities after moderate and severe TBI [
10]. In addition, Jacobsson et al. demonstrated reduced quality of life and impairment after moderate to severe TBI compared with a normative reference sample [
16]. Interestingly, in the present study we did not find a significant difference in the quality of life measured by SF-12 between the different TBI groups despite the reported increased impairments measured by GOS. This is in contrast to other studies and might be based on the fact, that we aimed to compare the three severities of TBI rather than matching one of them to a normalized population as other studies did [
10,
16]. In this context, a profound influence or diminished quality of life due to mild TBI 10 years after injury is debatable in the current literature: Accordingly, Sadowski-Cron et al. revealed persisting complaints such as headache, concentration deficits and somatic complaints [
8]. Furthermore, Zumstein et al. were able to verify mild TBI impacting life quality 10 years after trauma considerably due to posttraumatic somatic syndromes [
3]. These complaints have been demonstrated to result in reduced SF-12 scores compared to normative population [
9].
Unemployment is known as a significant problem following TBI [
3,
10]. According to the presented results, severe TBI resulted in a significant occupational decline followed by loss of salary. Interestingly, the demonstrated comparable unemployment status between the different TBI groups has not been found in the current literature: Grauwmeijer et al. revealed that patients after moderate and severe TBI with impaired cognitive functioning at hospital discharge were at high risk of long-term unemployment three years later [
23]. These findings were supported by the long-term follow-up study of Jacobsson et al., whose patients with moderate to severe TBI had increasing unemployment rates compared to mild TBI [
16]. However, these studies evaluated unemployment rates up to 44% after severe TBI which seems considerably higher compared to the presented rate of approximately 13%. Comparability to the presented results could be limited due to increased disability rates measured by GOS: The authors found up to 80% of patients with severe TBI had a GOS less than 4 points meaning that 80% were severely disabled [
16,
23] while permanent disability in the presented study was revealed only in 5.6%. Furthermore, it might be assumed that significant reasons for these diverse results are found in the different health care and social systems [
24], which make an international comparison and a prediction of the long-term vocational impact of different TBI severities difficult.
The presented study has several limitations. Due to the follow-up period of at least 10 years, many critical events might have occurred in a persons’ life potentially affecting outcome. Although the participating patients have been asked for life-changing events between the TBI and follow-up, this aspect has to be considered as a potential limitation when interpreting the results. Especially pre-existing psychological and behavioural problems might be missed by this study, because none of the traumatized patients was assessed by specific psychological scores on admission when treated for TBI. We excluded patients with mental handicaps previous to TBI, but minor psychological problems were potentially missed by this study. As these problems might interfere with the presented outcome results, this aspect should be taken into account when interpreting the presented results.
Another major limitation is to be mentioned by including pediatric trauma patients to the study population. Pediatric TBI is known to have a better physical outcome compared to adult patients due to the plasticity of the immature brain [
11,
17,
25‐
31]. Although this aspect is not proven in the literature without remaining criticism [
11,
17,
25‐
31], this study could have been biased considerably. However, we demonstrated the contingent of children between the TBI groups as statistical comparable reducing the bias effect. Nevertheless, results should be interpreted carefully due to this limiting factor.
Furthermore, the length of follow-up and data collection at a single center and its retrospective design might be a limitation and it is likely that the presented findings cannot reflect the advances made in acute care as well as rehabilitation during the last decades. Additionally, one might be aware of a potential selection bias due to the large number of excluded patients which is a known limiting aspect of long-term outcome studies discussed previously.
Acknowledgements
The authors thank Dr. Nicola-Alexander Sittaro, MD, for supervising the study in the early phase.
This study is part of the doctoral thesis of Mrs. Julia Urner, Trauma Department, Hannover Medical School, Hannover, Germany, and Mrs. Ezin Deniz, Trauma Department, Hannover Medical School, Hannover, Germany.
Author disclosure statement
Industrial support was provided by Hannover Life Re-Insurance, Hannover, Germany. Dr. Nicola-Alexander Sittaro, MD, and Dr. Ralf Lohse, PhD, Hannover Life Re-Insurance, Hannover, Germany, gave advice. No direct or indirect financial support or other assets were transferred to the authors for this study. The authors state that there are no competing interests.
Competing interests
Industrial support was provided by Hannover Life Re-Insurance, Hannover, Germany. Dr. Nicola-Alexander Sittaro, MD, and Dr. Ralf Lohse, PhD, Hannover Life Re-Insurance, Hannover, Germany, gave advice. No direct or indirect financial support or other assets were transferred to the authors for this study. The authors state that there are no competing interests.
Authors’ contributions
HA conceived this study designing the trial, provided statistical advice on study design, analyzed the data and drafted the manuscript. CP, OG, RL and MF provided statistical advice on the study design, analyzed the data and supervised the conduct of the trial and data collection. JU and ED conceived the study and designed the trial. CZ conceived the study, designed the trial, obtained research funding and supervised the conduct of the trial. FH conceived the study, designed the trial, obtained research funding, supervised the conduct of the trial and data collection, provided statistical advice on study design and analyzed the data. HA takes responsibility for the article as a whole. All authors contributed substantially to manuscript revision. All authors have read and approved the final manuscript for publication.