Photosensitivity and Pain in Complex Traumatic Brain Injury
Abstract
Chronic pain is a significant clinical problem, reported by about half of Veterans seeking care through the Department of Veterans Affairs (VA) system. Veterans that have sustained a traumatic brain injury (TBI) are particularly likely to experience chronic pain. The chronic pain experienced by these Veterans is also associated with marked fatigue and sleep difficulties, which can further diminish their psychological and physical function and well-being. Acute pain can usually be controlled using pain-relieving drugs. However, chronic pain can be extraordinarily difficult to treat and cannot always be tied directly to activation of normal pain sensors in the body. This pain is instead thought to be due to “sensitization” of pain-processing circuits in the spinal cord and brain. In the sensitized state, pain pathways in the brain and spinal cord become abnormally responsive and are activated by inputs that would not cause pain in most people. As a result, everyday stimuli such as a gentle touch or normal light levels are experienced as painful. The idea of sensitization is well supported by animal studies, where experimental techniques can be used to identify increased responsiveness of pain pathways in the brain. Unfortunately, sensitization cannot be demonstrated so easily in humans. Nevertheless, more than half of Veterans returning from Iraq and Afghanistan with TBI complain of abnormal sensitivity to light. We believe that this heightened photosensitivity could be a window into pain in the brain. This is based on our recent demonstration that a specific population of pain-enhancing brain cells can respond to light. Because activation of these brain cells causes the pain threshold to be lowered, light could cause normal stimuli to be felt as painful. Consistent with this idea, many chronic pain patients avoid bright light and complain that light is bothersome. In addition, in some chronic pain patients, light can activate brain networks considered to signal pain. Taken together, these lines of evidence suggest that photosensitivity could be a useful marker for sensitization in Veterans with chronic pain and complex TBI. Our overall hypothesis is that, due to aberrant engagement of pain-enhancing brain cells by light, Veterans with complex TBI will be more sensitive to light and experience more pain than non-trauma exposed Veterans. Our objectives are to quantify photosensitivity in Veterans with complex TBI and determine whether photosensitivity is associated with greater pain, poor sleep, and poor functional outcomes. We will also use functional imaging to determine whether a dim light stimulus can activate the pain-related brain regions in Veterans who have suffered a TBI, but not in pain-free controls. This would be strong evidence that pain pathways in the brain are sensitized after TBI. If we are correct, photosensitivity could serve as a quantitative marker of sensitization in Veterans with complex TBI, guiding their treatment and serving as a measure of their responses to different therapies. This work would also provide a better understanding of the brain mechanisms of pain in individual Veterans with chronic pain, giving us a simple, inexpensive test that could be applied in a standard clinical setting. Because this test would provide us with a window into brain function, this could guide pharmacological treatments that act directly upon these brain mechanisms and reduce the need for unnecessary surgical procedures or chronic non-specific opioid use. Finally, these studies could pave the way for modifying the light environment as a way to improve pain, functional outcomes, and quality of life for these Veterans.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 29, 2018
- Source ID
- W81XWH1710423
Entities
People
- Mary Heinricher
Organizations
- Oregon Health & Science University
- United States Army