Family Health: Traumatic brain injuries may result in chronic pain

The Centers for Disease Control and Prevention estimates that about 1.4 million Americans suffer traumatic brain injury every year. Traumatic brain injury is defined as a non-degenerative, non-congenital insult to the brain from an external mechanical force, possibly leading to permanent or temporary impairment of cognitive, physical and psychosocial functions, with an associated diminished or altered state of consciousness.

Pain is a common concern after suffering a brain injury. This pain is usually self-limiting and resolves as tissues, like strained muscles or fractured bones, heal. Sometimes, however, pain lingers beyond the time frame expected for the injured tissues to heal. We call this type of pain chronic or persistent pain. Pain is typically considered chronic if it lasts longer than three to six months.

There appears to be a link between traumatic brain injury and the development of chronic pain. It also appears that individuals who have had a mild brain injury tend to develop chronic pain syndromes at a higher rate than those with more severe types of brain injury, but the reason for this is unknown. Chronic pain after traumatic brain injury can take the form of headache and migraine, musculoskeletal pain (neck pain, low back pain), visceral pain (abdominal pain, irritable bowel syndrome) and nerve pain (complex regional pain syndrome, neuropathies). Post-traumatic headache is the most common form of chronic pain after a head injury, and this type of headache is often debilitating. People with pre-existing headache syndromes are particularly susceptible to recurrence or worsening of headache after a traumatic brain injury.

It can be difficult to predict if pain will transition from acute to chronic in any one person. Factors that can contribute to the development of chronic pain include psychological comorbidities such as anxiety and depression; physical, emotional or socioeconomic stress; sleep disorders; a history of chronic pain conditions like fibromyalgia or migraine; and a history of trauma, including traumatic brain injury. Treating chronic or persistent pain can also be difficult. One reason for this is that we are still trying to understand how chronic pain works.

Neuroimaging studies of individuals with chronic pain show both functional and structural brain changes that suggest the brain has learned different ways to process sensory information from the painful area. There is also evidence that the brains representation of the painful area can change, causing perceptual disturbances, like difficulty telling where someone is touching you (tactile acuity) or difficulty telling left from right when looking at images of the painful area (laterality).

These findings have led to the theory that the painful sensations experienced during chronic pain may have both peripheral and central contributions.

For example, when an area is injured it becomes inflamed (red, warm, swollen and painful). At first, inflammation is beneficial and can help the area heal. If inflammation continues for long periods of time, however, the receptors in the area that detect tissue injury (nociceptors) can change and become hyperexcitable, or more easily stimulated. This is called peripheral sensitization.

Peripheral sensitization can lead to a wind up phenomenon spreading hypersensitivity from the receptors along the nerves to the spinal cord and eventually to the brain, where the activity of neurons is altered. In a gross simplification, the receptors start to overreact to stimuli in the painful area, causing the nerves to overreact to the receptors and ultimately leading to an overreaction by the brain to the information from the nerves. If this goes on long enough, the nervous system can adapt to being wound up and change the way it responds to stimuli.

The nervous system can learn to react to painful stimuli, like a muscle spasm or bruise, as if it were much more painful than it is (hyperalgesia) or it can learn to react to completely normal stimuli, like movement or touch, the same way it would react to injury, by producing pain (allodynia). Hyperalgesia and allodynia are hallmarks of chronic pain. Peripheral and central sensitization and subsequent hyperalgesia and allodynia are maladaptive processes that may occur more easily in a nervous system that is healing from a traumatic brain injury.

Early identification and intervention is the current best practice recommendation for the treatment of chronic pain especially in individuals with traumatic brain injury. For example, people with post-traumatic headaches are being treated more aggressively and earlier on then they have in the past with good outcomes.

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Family Health: Traumatic brain injuries may result in chronic pain