Mood and Anxiety Disorders Following Traumatic Brain Injury

Military TBI

TBI has been described as the "signature wound" of Operation Iraqi Freedom and Operation Enduring Freedom in Afghanistan. Modern body armor has greatly reduced the frequency of severe injuries to the thoracic and abdominal regions. Consequently, injuries to the head and the extremities are the predominant wounds encountered in contemporary battlefields. The use of Kevlar helmets has significantly reduced the frequency of penetrating head injuries, making closed head injury (eg, from blasts, motor vehicle accidents, or falls) the most frequent form of TBI observed in current military operations.²⁷

According to military records, blast injuries constitute the most frequent type of injury observed, accounting for approximately two-thirds of war-zone evacuations.²⁷ A recent study reported that 88% of soldiers treated at a medical unit in Iraq were injured by improvised explosive devices or mortar fire.²⁸ The vast majority of injuries (97%) observed among the troops of a Marine unit in Iraq were produced by improvised explosive devices or mines.²⁹ In addition, it has been estimated that 59% of soldiers with blast injuries have sustained a TBI.³⁰ As of March 2006, 28% of all injured troops in these conflicts had a TBI, with blast being the cause in most cases (88%).²⁷

The troops in Iraq and Afghanistan are different from other military groups and from civilian populations at risk for a TBI. In contrast to other conflicts (eg, the Vietnam War), deployed military forces in Iraq are all-volunteer, professional troops. A recent study reported on the demographic characteristics of a large cohort of soldiers in Iraq. About 90% of the troops were men in their 20s; 56.4% were white, 16.2% were black, 14.7% were Hispanic American, 2.6% were Asian American, and 10.1% were other. About half (45.4%) were married and most had a high school education (mean [SD], 12.5 [1.3] years).³¹ Overall, military samples were found to have better psychosocial adjustment than civilians with a TBI.²⁷ Within the military cohort, 6% reported past psychiatric disorders, and 4.2% reported past alcohol use disorders. The rates for alcohol abuse were significantly lower than the ones observed in civilian samples.^11,12

Although psychiatric disturbance will certainly have a negative impact on the clinical recovery and quality of life of injured veterans, the frequency, phenomenological characteristics, and clinical correlates of mood and anxiety disorders that occur after a TBI have not been thoroughly described among veterans returning from Iraq and Afghanistan. Lew and colleagues³² reported on 2 cases of veterans with mild head injuries who, although they were initially judged fit to return to light duty, experienced dramatic personality changes 3 to 5 months after the TBI. A comprehensive battery of neuropsychological tests and electrophysiological measures revealed significant impairments on tasks probing complex attentional functions, speed of in- formation processing, and problem-solving ability.³² Unfortunately, the impact of mood and anxiety disorders on neuropsychological performance was not assessed. The investigators concluded that these 2 cases are paradigmatic of a growing number of veterans referred to their rehabilitation center.

Previous epidemiological studies suggest that there is a high prevalence of mental health disorders among military personnel in Iraq and Afghanistan.^33,34 A recent study of 103,788 veterans first seen at the Veterans Affairs Health Care System (VA) following active duty in Iraq and Afghanistan reported that about 25% of all veterans received a mental health diagnosis.³⁵ The median time from service separation to the first VA clinic visit (mostly in primary care settings) was 2.9 months after separation, and the most frequent diagnoses were PTSD (13%) and mood disorders (11%). In another recent study, Hoge and colleagues³⁶ examined the frequency of mood and anxiety disorders following a mild TBI in 2525 US soldiers returning from Iraq. PTSD was strongly associated with the occurrence of a mild TBI (Table 2). Soldiers with a mild TBI were more likely to have poorer medical outcomes. More important, PTSD and depression were most frequently linked to poor outcomes.

It must be noted that assessment of a mild TBI in the context of military operations is difficult for multiple reasons, including retrospective bias and the fact that alterations of consciousness (a decisive criterion in the traditional definition of a mild TBI) may be part of an acute stress reaction rather than the consequence of a traumatic injury. This may result not only in an overestimation of the number of TBI cases but also in a biased estimate of the strength of the association between a TBI and PTSD, given that acute stress reactions are a significant predictor of later PTSD. However, the stronger relationship of psychiatric illness with a history of loss of consciousness suggests that subtle forms of brain damage may contribute to the genesis of these disorders. Assessment of the type, location, and extent of these brain alterations requires the use of more sensitive neuroimaging techniques such as diffusion tensor imaging, functional MRI, or magnetic resonance spectroscopy. Cognitive dysfunction is a major contributor to disability following a TBI. Neuropsychological changes following active duty in Iraq and Afghanistan were examined by the Neurocognition Deployment Health Study. The investigators concluded that deployment to Iraq was associated with increased risk of neuropsychological deficits.^31,37 However, the relationship of these cognitive changes to the presence of mood and anxiety disorders has not been adequately studied and constitutes one of the priorities of research in this field. Is a TBI a significant risk factor for mental health problems following active duty in Iraq or Afghanistan? Are the phenomenological presentation and clinical course of psychiatric disorders that occur after a TBI different from those observed in patients without brain damage? These important clinical questions require more extensive investigation. Furthermore, the physiopathology of blast injuries, particularly in the case of recurrent exposure to blasts, has not been fully elucidated and might be substantially different from the mechanisms described in other forms of TBI. This pathophysiology may be contributing to differences in the clinical presentation of these TBI patients. For example, preliminary studies that compare blast versus nonblast closed head injuries among veterans admitted to the Walter Reed Army Medical Center suggest that patients injured in a blast are more likely than those with a nonblast TBI to present with acute stress reaction and PTSD.²⁷

Conclusions

TBI has been associated with an increased frequency of psychopathological disorders in both civilian and military populations. Disruption of prefrontal circuits regulating mood and emotional processing is an important causative factor in the genesis of these syndromes. In addition, mood and anxiety disorders account for a significant part of disability resulting from TBI of varying severity. Thus, there is an urgent need to study clinical characteristics, mechanisms, and treatment alternatives for these conditions. In turn, the information obtained from patients with brain injuries may provide further insight into the pathophysiology of these disorders in the population as a whole.