Advancing Rehabilitation: Physiological, Psychological, and Neuroimaging Measures of Factors That Predispose, Promote, and Perpetuate Posttraumatic Dizziness

Objectives and Rationale: Each year, about 1 in 130 Americans experiences a traumatic brain injury (TBI). Actual numbers may be higher because many are not reported. About four out of five TBIs are mild (mTBIs), and most people with mild injuries recover, but about 10-20% do not. Dizziness is one of the most disabling symptoms in people with histories of mTBIs. People with post-mTBI dizziness are less likely than other people with mTBIs to return to daily activities. That includes military Service members who are less likely to return to duty. We do not know why dizziness is so troublesome or what causes it to become a chronic problem. Acutely, TBIs may cause damage to the inner ear or parts of the brain that control balance, but over the long term, there is very little connection between the initial injuries and ongoing symptoms. Although it made sense to focus research on the vestibular (balance) system in patients with post-mTBI dizziness, those investigations did not provide much understanding of the cause of long-term symptoms or guidance to develop specific therapies. Some experts suggested that psychological problems like post-traumatic stress are responsible for long-term dizziness. That idea may have merit too, but it offers no better ideas about which brain mechanisms might go awry.

Over the last 30 years, a more sophisticated concept has emerged from research on chronic dizziness in people who do not have TBIs. This new concept suggests the chronic dizziness is not usually the result of an acute physical injury alone or psychological factors alone, but rather how they interact during crucial time periods to transform acute symptoms into chronic ones. Two physiological mechanisms have been identified: stiffened postural control and over-reliance on visual stimuli for spatial orientation. Recent research using high-tech brain imaging (functional MRI [fMRI]) found that areas of the brain that give us our sense of spatial orientation may not be as active in patients with a type of chronic dizziness called persistent postural-perceptual dizziness (PPPD) as they are in healthy people. The symptoms of PPPD overlap with the worst type of post-mTBI dizziness.

The goal of this study is to bring these recent advances to the field of TBI. We will enroll people who have dizziness lasting for 2-8 weeks after mTBI. We will evaluate them with tests of physiological and psychological functioning and use the fMRI techniques that we developed in our previous work to look for changes in brain structure and function. After that, we will search for combinations of clinical and brain imaging variables that predict good or bad outcomes at 6-8 months after injury, when we will retest our participants.

Potential Impact of the Research: This project is designed for the 10-20% of people with post-mTBI dizziness who do not recover quickly.

Potential Clinical Applications: We expect the results of this study to have two potential clinical applications. The first will be better triage during the post-acute period (2-8 weeks after injury) when most people will have recovered, but the ones that we will be studying may be starting to settle into a chronic phase of illness. The second clinical application will be new therapies designed around specific pathological mechanisms. Current treatment focuses on symptom control, which is important, but has limited effects without a good understanding of physiological and psychological processes that drive symptoms and the changes in brain functioning that are associated with them.

Timeline to Achieve Patient-Related Outcomes: The next step will be clinical trials of post-acute triage processes that incorporate the results of this project into clinical management. Testing and refinement of advanced triage methods could be completed in 2-4 years. We also plan to develop new treatment strategies based on mechanisms of illness that we expect to discover in this study. Development and testing of new treatment strategies would likely require 3-6 years.

Likely Contributions to Advancing the Field of Complex TBI: The results of this project will extend beyond these two clinical applications. As was the case with PPPD, we expect this line of investigation to shed new light on mechanisms of chronic dizziness that follows mTBI.

Benefits to Military Service members, Veterans, and Others Living with Complex TBI: We will study civilian groups in this project as we did in our preliminary work, but we expect our next steps, that is, our clinical trials of improved triage protocols and novel therapies, to take place in military and Veterans Affairs medical centers as well as civilian institutions. Better triage processes and mechanism-specific treatments should offer cost-effective advanced treatment to patients of all types who struggle with dizziness after mTBIs. Finally, we expect our next set of advanced brain imaging studies to include Service members and .......