Effective Treatment of Migraine: New Research on Cutaneous Allodynia
Most people have had headache at some point in their lives. The headaches that we have all experienced tend to be mild in severity, last less than a day, and typically don’t interfere with activities. We are able to get to work, cook a meal, talk with friends, and help with our children’s homework. We tend to think well of ourselves because we were able to tough it out, and it wasn’t a big deal for us.
For some others, the headaches are much worse. Headaches may occur for days. People with more frequent or severe headaches may be unable at times to do usual daily tasks. They never know whether they may spend the day vomiting, or being unable to get out of bed. They can’t plan on being able to drive safely to pick up their children from school, or to make that sales meeting.
What causes headaches to progress in some cases, and not in others?
Recent research by Rami Burstein at Beth Israel Deaconess Medical Center in Boston, and at Massachusetts General Hospital, has thrown light on why some headache patients worsen over time. I met Dr. Burstein recently at a conference and discussed this interesting research with him. The research describes how the brain becomes “sensitized” during attacks of migraine. When this sensitization occurs, patients are more likely to have further headaches; and, possibly, are more likely to have other pain syndromes such as TMJ problems or fibromyalgia.
Dr. Burstein studied skin sensitivity during the development of a headache by measuring the pain thresholds in the head and forearms bilaterally at several time points during a migraine attack in a 42-year old male. This patient was experiencing sensitivity to noise, light, and odors during a migraine, with nausea progressing to vomiting, worsening of the headache by coughing or movement, and pain when simply combing his hair or touching his scalp (“cutaneous allodynia”).
Comparisons between his pain thresholds in the absence of migraine, and at onset of migraine, revealed the following:
• After one hour, sensitivity to pressure and cold (“mechanical and cold allodynia”) started to develop on the same side of the head but not at any other site;
• after two hours, sensitivity spread to the forearm on the same side and the head on the opposite side;
• after four hours, sensitivity to heat was also detected while sensitivity to pressure and cold continued to increase.
According to Dr. Burstein, this suggests that the trigeminal nerve, which supplies the blood vessels in the face and in the coverings of the brain, begins firing excessively associated with the onset of pain. This barrage of impulses activates neurons in the brain, which become progressively sensitized, resulting in a lowered pain threshold. It is this induced lowered threshold, or sensitivity, of pain receptors in the brain that leads to the
findings of sensitivity to light, noise, odors, light touch, pressure, or temperature changes on the skin. Like having your hearing aid on too high, the receptors “SQUEEEEEEEK” when they receive any sensory input. The sensitivity gets turned way up.
Using threshold testing, we have begun to explore the changes that occur during chronic headache in our own patients. In this test of pain fiber transmission, the current is applied with a cotton applicator dipped in a saline solution, and the sensitivity is increased until the patient first reports being able to feel the tingling sensation.
This threshold is measured and recorded in each branch of the trigeminal nerve that supplies the face. In many instances, chronic headache appears to be associated with changes in the ability to detect a microvolt current applied to the face. In some cases, sensation has been lost, corresponding to long-term damage to pain fibers (called a-delta fibers) that transmit pain during headache. In other cases, the fibers are overly sensitive, corresponding to the changes Dr. Burstein has reported in his laboratory.
Increased sensitivity is demonstrated when the patient can detect currents as low a 8 microvolts; in decreased sensitivity, currents are not detected below 30 microvolts, and in some cases the threshold is much higher, indicating long term a-delta pain fiber pathway damage.
The changes that occur in the brain, that lead to long-term increase in sensitivity in pain-receiving areas there, add further experimental weight to many other converging lines of evidence (such as small areas of damage on MRI, and of further evidence of increased stroke risk in patients with long standing headache) to indicate that frequent headaches may produce neurological damage. That damage may impair the ability of the brain to reset itself, to bring the pain threshold back to normal.
Treating Sensitized Brains
Losing the ability to return to normal sensitivity of the brain appears to explain why some patients do not respond to standard treatment, or who may go on to develop other complications associated with chronic headache—depression, sleep disturbance, TMJ and fibromyalgia pain syndromes, lack of response to medication or sensitivity to side effects, and reduced ability to regulate vascular tone (perhaps predisposing to stroke).
Patients with migraine may not have been asked about other pain symptoms. Symptoms such as sore muscles or joints, tenderness of the neck, scalp sensitivity, burning oral or vaginal mucosa, fibromyalgia, chronic and poorly explained jaw pain, “arthritis,” sore feet or plantar myofasciitis, sinus sensitivity, and a number of other chronic pain symptoms, often go by many medical names, but may all be related to this brain sensitivity that underlies migraine. Even when another problem such as arthritis of the neck exists, treatment of the underlying sensitivity to pain may significantly improve sensitivity to the other pain condition.
Perhaps most importantly, patients with chronic headache will often come to the Headache Clinic with a grab-bag of diagnoses, and leave with one diagnosis. The changes that underlie chronic headache are simple, but the symptoms they may cause are complex and serious. And often, successful induction of a remission of chronic headache is associated with a return to normal of brain sensitization, and recovery from these other problems as well.
For more information on headaches, as well as links to the National Headache Society and the American Council on Headache Education, see us on the web at www.ncheadaches.com.
The North Carolina Comprehensive Headache Clinic
provides diagnostic evaluations and treatment for the patient with headache. For more information, contact: NORTH CAROLINA COMPREHENSIVE HEADACHE CLINIC 2501 Atrium Drive, Suite 400 Raleigh, NC 27607 Telephone: (919) 781-7423 www.ncheadaches.com
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