The Military and mild TBI

Definition of MTBI

Due to its particular relevance to the current conflicts in the Middle East, mTBI has been described as the “signature injury” of the Afghanistan and Iraq wars (Okie, 2005). In this context, mTBI is characterised by a “brief loss of consciousness or altered mental status, as a result of deployment‐related head injuries, particularly those resulting from proximity to blast explosions” (Hoge et al., 2008, p.454). This definition is consistent with those widely cited in research (Carroll, Cassidy, Holm, Kraus, & Coronado, 2004) and is used as a basis for American military screening programs (Defense and Veterans Brain Injury Center, 2009).

Symptoms of MTBI

Symptoms that can occur following mTBI include problems with memory, balance, sleep and concentration, headache, tinnitus, sensitivity to light or other visual disturbance, fatigue and irritability (Bryant, 2008; Fear et al., 2009). A small proportion of individuals continue to have difficulties weeks or months later; estimates of those with persisting symptoms have been as high as 20% but comprehensive reviews report that 5% is likely a more accurate figure (Carroll et al., 2004; McCrea et al., 2009).

 

 

 

 

 

 

Prevalence

Accurate prevalence estimates of MTBI are extremely difficult to ascertain given the non‐specific nature of post‐concussive symptoms (Fear, et al., 2009; Powell, 2008; Stein & McAllister, 2009). There is a large degree of overlap between symptoms of MTBI and symptoms of psychiatric disorders like depression and post‐traumatic stress disorder (PTSD; American Psychiatric Association, 1994) which can be misattributed to mTBI.

Prevalence estimates of mTBI also vary between countries. In general, the United States has reported a higher prevalence of mTBI than the United Kingdom and Canada, particularly in studies employing MEAO‐deployment screening data (Brenner et al., 2010; Pietrzak, Johnson, Goldstein, Malley, & Southwick, 2009; Polusny et al., 2011; Schneiderman, Braver, & Kang, 2008; Terrio et al., 2009). A 2008 review, for example, reported that 12% to 20% of returned US personnel deployed to Iraq and Afghanistan met criteria for a mTBI episode following deployment (Thompson, 2008). In contrast, 4.4% of British personnel returning from Afghanistan and Iraq and 6.4% of Canadian military personnel returning from Afghanistan reported deployment‐related mTBI (Rona, Jones, Fear, Hull, et al., 2012; Zamorski, Darch, & Jung, 2009).

 

 

Why is the prevalence of mTBI difficult to establish?

Explanations that exist to account for the variation in reported rates of mTBI include measurement issues (to determine the degree of combat exposure (Rona, Jones, Fear, Hull, et al., 2012) and deployment length (Rona, Jones, Fear, Sundin, et al., 2012)) as well as cultural differences such as compensation practices and healthcare systems across countries (Hoge, Goldberg, & Castro, 2009; Rona, Jones, Fear, Hull, et al., 2012).

Aside from these differences across countries, determination of the prevalence of deployment‐mTBI is difficult in general owing to significant problems with the methods used to measure and diagnose mTBI (e.g., lack of reliable diagnostic tools (Hoge, et al., 2009) and reliance on retrospective self‐report of events involving loss of consciousness, awareness and memory (Belanger, Uomoto, & Vanderploeg, 2009; Polusny, et al., 2011)).

Accurate diagnosis of mTBI is further complicated by the fact that symptoms associated with mTBI are highly non‐specific and overlap greatly with many other conditions and syndromes, in particular, PTSD, depression and chronic pain. PTSD in particular shows significant overlap with deployment‐related mTBI. There is overlap in both symptom profiles and also aetiology; with the potential for both disorders to arise from the same combat experience.

Many research groups have explored the relationship between these two conditions with conflicting results. Hoge et al. (2008) found in their US infantry sample returning from Iraq that 32.6% of those reporting mTBI also met criteria for PTSD, while only 16.2% of those reporting other injuries and 9.1% of non‐injured met criteria. Similarly, 13% of those reporting mTBI met criteria for depression compared with 6.6% of those with other injuries and 3.3% of those reporting no injury. In their cross‐sectional survey of Iraq/Afghanistan veterans, Schneiderman et al. (2008) found a strong association between PTSD and post‐concussive symptoms, even after removing the symptoms that overlapped between the measures used; sleep difficulties and irritability.

Despite the lack of clarity in the literature on this subject, it is clear that psychiatric comorbidity must be considered when an individual presents with post‐concussive symptoms. Understanding mTBI in the context of deployment is important owing to the implications for healthcare provision, deployability status and compensation for affected veterans.

As such, there is a distinct lack of epidemiological estimates of mTBI in military populations, including the Australian Defence Force, that needs to be addressed.

 

 

 

 

 

US & UK Studies: Different contexts

The context of these findings One of the current difficulties in the literature is the strikingly different emphases that have emerged from the studies conducted in the US and the UK.

Most studies examining deployment‐related mTBI and associated post‐deployment functioning in Afghanistan and Iraq veterans have been conducted by American researchers (Brenner, et al., 2010; Hoge, et al., 2008; Pietrzak, et al., 2009; Polusny, et al., 2011; Schneiderman, et al., 2008; Terrio, et al., 2009).

There has been a major focus on the neural and cellular consequences of mTBI in the US literature (e.g., Davenport, Lim, Armstrong, & Sponheim, 2012). Often this literature fails to explore the related neuropathology of PTSD which may interact with, and explain some of these abnormalities. The high profile of mTBI in the US has also influenced healthcare provision and compensation policies for American military personnel (Hoge, et al., 2009).

The findings in Annex 1 which allow a comparison of the ADF with the report of Hoge et al. (2008) demonstrate the very high rates of PTSD in the US veterans with and without mTBI and the need for caution in directly applying US recommendations to the Australian setting without careful consideration. Researchers from the UK have published investigations on head injury in military personnel from Iraq (Fear, et al., 2009) and have also recently published data relevant to military personnel in both Iraq and Afghanistan (Rona, Jones, Fear, Hull, et al., 2012). These studies have highlighted the nonspecific nature of post‐concussive symptoms and the fact that other exposures readily explain their occurrence. This emphasis is similar to the Canadian (Zamorski, et al., 2009) and Dutch (Engelhard, Huijding, van den Hout, & de Jong, 2007) research that has published data related to  military personnel in Iraq and Afghanistan. The findings of this report are consistent with this position.

The difference between the US and UK positions is perhaps best characterised by the conclusion stated in the review of the UK group about the history of shell shock and mTBI (E. Jones, Fear, & Wessely, 2007). They concluded that: “disorders that cross any divide between physical and psychological require a nuanced view of their interpretation and treatment. These findings suggest that the hard‐won lessons of shell shock continue to have relevance today.” This review highlights the importance of caution in this domain as there may be a propensity for concussive injury to be over simplified as the cause of post‐deployment symptoms. This report needs to be considered in the light of these conclusions.