Central to the present study is the question of how the development of PTSD in patients with TBI is influenced by extended loss of consciousness. In order to investigate this, two groups of patients were formed and compared. The first group consisted of people who had either not lost consciousness during the event or were unconscious for less than one hour. This group was compared to a sample of those who had lost consciousness for twelve hours or more. It was assumed that in cases in which unconsciousness lasted less than 1 hour there would still be sufficient islands of memory of the accident itself. According to reports of the participants in the present study, this assumption proved to be correct. In order to ensure that differences in the incidence of PTSD symptoms were not due to other characteristics, the two groups were also compared with regard to age at the time of the accident, current memory functioning, and severity of injury. The groups did not differ significantly with regard to age or memory functioning as indicated through the WMS-6. There was a significant difference in severity of injury as measured through the AIS: those patients who had experienced loss of consciousness sustained more severe injuries. Since this group was less likely to develop PTSD, severity of injury did not prove to be a contributing factor.
Incidence of PTSD in patients with TBI
Of the sub-sample of patients with extended unconsciousness, 3 % were diagnosed with PTSD. This is considerably lower than the prevalence rates for other traumatic experiences where victims remained conscious, including traffic accidents (16.5 % according to Ehlers et al. [12
]), war crimes (22% [14
]), rape (50 %) and other forms of assault (25 % [13
]). It is also below the 5% (men) or 10% (women) lifetime prevalence for PTSD in the USA [20
]. In contrast, the 27% point-prevalence in the TBI-group without extended unconsciousness corresponds well with the typical point-prevalence after traumatic stress experience in other studies.
However, in this sample it has been shown that PTSD does indeed occur in patients who have sustained a traumatic brain injury. The two disorders are not mutually exclusive. However, PTSD occurs less frequently than in patients who have suffered more severe types of traumatic events. The duration of unconsciousness explains the variance and the low occurrence rates. Obviously, loss of consciousness has a protective effect with regard to the development of PTSD. Larger sample sizes would be needed to determine if loss of consciousness consistently prevents the development of PTSD.
Finally, it is of great importance for the clinician to be aware of the possibility of the development of PTSD, especially in patients who did not sustain severe organic brain damage. In certain cases, psychologically related symptoms may be erroneously attributed to organic causes.
Forms of reexperiencing
It has also be shown in this study that intrusive memories and nightmares occurred more often in patients who had not lost consciousness during the event. Intrusions in these patients related more to the accident itself, rather than to events occurring shortly before or after the accident. Finally, these patients were more like to report re-experiencing bodily sensations and feelings similar to those during the accident, as well reporting times in which they had the impression that the event is still occurring in the present. On the other hand, patients who had lost consciousness during the event were more likely to report experiencing an internal narrative of the event. This was never the case in patients who had been conscious. Thus, it could be shown that loss of consciousness has an influence on the frequency and the form of intrusive memories.
There was no support for the assumption that patients who had been unconscious at the time of the accident would experience more intrusions of the events occurring before or after the accident. While this did happen, it was not more frequent than in patients who had been conscious. As hypothesized, intrusions through reports from others were more frequent in patients who had sustained loss of consciousness. However, this difference was not significant.
Patients who had been diagnosed with PTSD also scored high on measures of anxiety and depression using the HSCL. This corresponds to findings from other studies which have found a high degree of comorbidity for these disorders [21
The two groups of patients (conscious – unconscious) did not differ with regard to level of depression. However, there was a significant difference in the scores that indicated anxiety symptoms, with the "conscious" group scoring significantly higher on measures of anxiety than the "unconscious" group. Apparently, conscious processing or memory of the event is required for the development of both anxiety symptoms and PTSD. Given the many causes of depressive symptoms, the lack of significant differences between groups comes as no surprise with the present sample size.
Limitations of the study
All patients from the present study were inpatients of a neurological rehabilitation unit. Thus, the findings may not be representative of other patients who have suffered from a TBI. Generally, patients still had neurological problems or physical handicaps, which may explain their vulnerability to the development of psychopathology. This, however, is contrasted by the lack of PTSD after severe loss of consciousness. It should also be noted that due to the nature of this study, there is no proof for causality, i.e. it may not be the loss of consciousness that prevents PTSD but some other factor that may be related to both a PTSD-resilience as well as a vulnerability to falling unconscious.