Postconcussion Symptom Checklist. Criteria for PTSD were met by 9 (20%) of the mild-TBI patients and 15 (25%) of the controls. In analyses comparing patients who had mild TBI and PTSD with those who had mild TBI alone, concentration deficits, dizziness, fatigue, headache, sensitivity to sound, and visual disturbances occurred statistically significantly more often in the mild-TBI patients who had PTSD. Among controls, concentration deficits and irritability were reported statistically significantly more often in PTSD patients than in those without PTSD. In the mild-TBI group, irritability was more common in individuals diagnosed with PTSD than in those who did not.

Creamer et al. (2005) studied 307 individuals who were admitted to a level 1 trauma center to determine the occurrence of PTSD and to assess the relationship between mild TBI, amnesia, and PTSD. Study criteria for mild TBI included LOC of up to 30 minutes, a GCS of 13 or more after 30 minutes, and PTA for up to 24 hours; these criteria were met by 189 (62%) of the subjects. Twelve months after injury, PTSD was diagnosed by trained mental-health clinicians using the Clinician-Administered PTSD Scale for DSM-IV. At 12 months after injury, 10% of the sample met criteria for PTSD: 15% with mild TBI and 7% without TBI (p = 0.1).

To the degree that mild TBI is being operationalized as altered mental status or brief LOC marked by “losing time,” that raises concern about differential diagnosis of dissociative phenomena, which can characteristically follow an emotional trauma in the absence of a TBI. Dissociation is characterized by a disruption in the integrated functions of consciousness, memory, identity, or perception of the environment. Consequently, ascertainment of mild TBI in contexts in which emotional trauma is likely to co-occur is complicated by potential misclassification of dissociation. That is of particular concern because dissociation at the time of trauma is a known risk factor for PTSD, and the co-occurrence constitutes a potential limitation of both the mild-TBI studies that follow. A recent study by Hoge et al. (2008) examined consequences of mild TBI in US soldiers in two brigades in Iraq that saw a high level of combat during a year-long deployment. About 3–4 months after returning from Iraq, 4,618 soldiers were sent a questionnaire covering injury sustained during combat, combat intensity, physical symptoms, major depression, and PTSD. Mild TBI sustained during combat was determined on the basis of the occurrence of at least one of the following three symptoms: losing consciousness (knocked out), being dazed or confused or “seeing stars,” or failure to recall the injury. Of the 2,714 soldiers who returned the questionnaire, 2,525 had complete responses: 124 reported mild TBI and LOC, 260 mild TBI and altered mental status, 435 other injury, and 1,706 no injury. There was a statistically significant association between mild TBI and high combat intensity, a blast mechanism of injury, more than one exposure to an explosion, and hospitalization during deployment. PTSD was present in almost 15% of the soldiers: 43.9% of those with mild TBI and LOC, 27.3% of those with mild TBI and altered mental status, 16.2% of those with other injury and 9.1% of those without injury (p < 0.001). After adjustment, PTSD was associated with mild TBI with LOC (OR, 2.98; 95% CI, 1.70–5.24) and with the highest quartile combat intensity compared to the lowest (OR, 11.58; 95% CI, 2.99–44.83).

Schneiderman et al. (2008) conducted a cross-sectional study of military personnel who had served in the conflicts in Iraq or Afghanistan to estimate the occurrence of mild TBI and the prevalence of PTSD and PCS and to examine associations of injury with PTSD and with PCS. The eligible study population included 7,259 veterans of Operation Iraqi Freedom (OIF) and Operation Enduring Freedom (OEF) who had left combat theaters by September 30, 2004, and were living in Northern Virginia, Maryland, Washington, DC, or eastern West Virginia in

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