The brain has no pain fibers (which is why patients undergoing epilepsy surgery are maintained in a conscious state and encouraged to verbalize responses to questions about what they see, hear and feel during pre-surgical brain mapping). However, the very same trauma that produces the brain injury often damages other parts of the body which house pain fibers, such as the cranial nerves and spinal cord. Closed head trauma can also inflame the meninges (the membranes which cover the brain) and cause migraine headache pain by abnormal expansion of meningeal blood vessels.
Trauma which violently jerks the neck or shoulder is known to cause stretch/strain damage to nerves in those areas, leaving scar tissue which sends pain signals along a cervical nerve root coming off the spinal cord in the neck or the brachial plexus in the shoulder region. Throbbing migrainous headache and burning neck or shoulder pain are not the only conditions that give rise to a CPD (chronic pain disorder).
CPD can result RSD (reflex sympathetic distrophy) or from limb loss. Phantom limb pain is constant and agonizing even years after the acute pain of the initial limb loss is long over. From application of MEG (magneto-encephalography) we know that the brain reorganizes its structure after limb loss, creating a zone of hyper-sensitivity which over-responds to the slightest touch of the portion of skin substituted for the lost limb. In some patients stroking of the skin on the face can trigger phantom limb pain. One theory put forward to explain this is that the brain abhors a sensory vacuum, and so when limb loss deprives the brain of input, it substitutes pain signals.
Traumatic loss of a limb is not the only trigger for reorganization of pain processing centers in the brain. We also know that chronic pain from chronic compression of a spinal nerve root can cause reorganization of the central nervous system with hypersensitivity. A recent study using SEP (somato-sensory evoked potential) showed that patients with chronic thumb pain in one hand from a C6 nerve root lesion, had undergone structural changes in their pain reception system (including thalamus, brainstem and dorsal horn of the spinal cord).
These changes made the patients perceive pain with any type of sensory stimulation of the affected area, even gentle touch, and electrical measurement of their brains confirmed their abnormal brain response objectively. J. Neuroscience 12/15/00 20(24):9277-9283. This research is very important, because it explains why a patient with CPD can continue to feel pain long after the visible effect of traumatic injury is gone (e.g. years after a herniated disc was surgically removed).
Treatment typically involves rest, pain medication (typically opiates), acupuncture, electrical devices to block pain signals such as TENS, psychotherapy and behavioral changes concerned with avoiding pain triggers. With severe, intractable pain, the patient is sometimes sent to a neurosurgeon for surgical removal of pain processing centers in the brain. A new avenue of promising research is the targeted delivery of a toxic substance (such as poison marine snail venom) to the cells in the spinal cord which relentlessly transmit pain signals.
The mode of delivery is attach the toxin to substance P, a chemical messenger. CPD is often accompanied by insomnia and depression. It can block and defeat TBI rehabilitation if not brought under good control by a physician skilled in management of chronic pain such as a physiatrist (a doctor of physical medicine and rehabilitation).
Top pain medicine clinics with comprehensive pain management programs include Stanford Hospital in California, UC Medical Center in San Francisco, the Mayo Clinic in Rochester, Minn., the Cleveland Clinic, Johns Hopkins Hospital in Baltimore, Md and the Mensana Clinic in Stevenson, Md. Our Links page has links to some of these clinics and a link to a comprehensive Pain Terms Glossary.