February 2005. Of those veterans, 2,235 (34%) returned the questionnaire, which included the Brief Traumatic Brain Injury Screen to detect mild TBI and the 17-item PTSD checklist. Twelve percent of the veterans who returned the questionnaire reported a history consistent with mild TBI. Mild TBI was most common among veterans injured by bullets or shrapnel, by blasts, in motor-vehicle crashes, in air or water transport, and in falls. About 11%(n, 250) of veterans were classified as having PTSD. Factors associated with PTSD included multiple injuries (prevalence ratio, 3.71 for three or more, 95% CI, 2.23–6.91) and combat mild TBI (prevalence ratio, 2.37, 95% CI, 1.72–3.28). PCSs were also associated with PTSD (prevalence ratio, 3.79, 95% CI, 2.57–5.59).

Secondary Studies

The committee identified 10 secondary studies that looked at the association between TBI and anxiety disorders, including PTSD, GAD, and panic disorder. The major limitation of many of these studies was a failure to include a comparison or control group. Other limitations include short followup time and use of small samples.

Three of the secondary studies examined PTSD occurrence after injury but lacked a control group or combined the mild TBI group with other injuries (O'Donnell et al., 2004; Gaylord et al., 2008; Sayer et al., 2008). O’Donnell et al. (2004) reported that 12 months after injury, approximately 20% of patients with mild TBI or other injury met criteria for one or more psychiatric diagnoses; PTSD and major depression were the most common. Similar numbers were reported by Gaylord et al. (2008); 18% of 76 service members had both mild TBI and PTSD. Warden et al. (1997) studied 47 active-duty service members who sustained moderate TBI and neurogenic amnesia for the event and found that none of the patients met the full DSM-III-R criteria for PTSD.

The nature of traumatic memories and their presence or absence may influence whether PTSD develops. Three secondary studies assessed what factors were associated with the development of PTSD after TBI. Gil et al. (2005) assessed the relationship between explicit memory of the traumatic event and the development of PTSD. They observed that respondents who recalled the traumatic event were 4.6 times more likely to have PTSD than those without memory of the event (95% CI, 1.1-9.9).

Two studies report on potential underlying mechanisms of PTSD in TBI. In a brain-imaging study, Koenigs et al. (2007) evaluated which specific areas of the brain were associated with PTSD in Vietnam veterans participating in the Vietnam Head Injury Study. They reported that PTSD was significantly less frequent in veterans who suffered damage to the ventromedial prefrontal cortex (18%) and amygdala (0%) than in those with damage outside these areas (40%) or those with no brain damage (47%). O’Donnell et al. (2007) examined whether tonic and phasic heart rate (HR) was predictive of PTSD in those who suffered trauma (including TBI). The authors observed that phasic HR relative to tonic HR and somatic arousal were the two predictors of subsequent PTSD. That suggests that the extent to which a person’s HR increases from resting when recalling the traumatic event is associated with the increased likelihood of PTSD.

Four secondary studies examined anxiety after TBI. Patients with mild TBI were more likely than limb-injured patients to report anxiety in one study (47.4% vs 14.1%; p < 0.0001) (Masson et al., 1996). Two other studies observed a similar prevalence of anxiety disorders after

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