The protein in the peripheral nervous system that gives mice the ability to sense cold and menthol has been identified, according to three recent journal articles. Menthol receptor TRPM8, as this protein is known, is found in humans and researchers believe these findings extend to people.
“[The receptor] provides a target for studying acute and chronic pain, as can result from inflammatory or nerve injury, the researchers say, and a potential new target for treating pain.
“’By understanding how sensory receptors work, how thresholds for temperature are determined, we gain insight into how these thresholds change in the setting of injury, such as inflammatory and nerve injury, and how these changes may contribute to chronic pain,’ says senior author David Julius, PhD, chairman and professor of physiology at UCSF.” (from UCSF press release, Detecting Cold, Feeling Pain: Study Reveals Why Menthol Feels Fresh)
Although the article only addresses pain caused by physical injury, it seems that the findings can apply to headache too. Nerves outside the brain, which are called peripheral nerves, become sensitized in both migraine and tension-type headaches. This is the source of allodynia — being sensitive to touch or feeling like your hair hurts.
Central Sensitization Determines Ideal Time for Migraine Treatment is the most reader friendly article that describes the role of peripheral nerves in migraine. I can only find basic information on tension-type headache and peripheral nerves. Do you know of any good resources on the topic?
I know I’m skimming the surface here. Any comments on the study or the role of peripheral and central sensitization in headache and migraine will be greatly appreciated.
KUOW, one of Seattle’s public radio stations, had a program yesterday on treating chronic pain with opioids with an expert panel weighing in. I only listened to the first half, but what I heard was informative and interesting.
They discussed a recent rise in overdoses among chronic pain sufferers. These are thought to be accidental, resulting from the need to increase dosages when the the patient develops tolerance.
Something I didn’t realize is that, according to the panel, most of the studies on opioids and pain focused on cancer pain, not chronic pain. There’s a significant distinction between medicating people with progressive, potentially fatal diseases and treating people with lifelong pain. Addiction and dependence are concerns, but tolerance — and the higher doses it requires — is a big risk too (not to mention potentially fatal).
Not covered in the program was that opioids appear to change the brain so that the patient actually becomes more sensitive to pain. Building tolerance is not only your body getting use to the drug (called desensitization), but you actually become more sensitive to pain overall (referred to as sensitization), not just the pain that you are specifically treating. It also increases allodynia, which is already a migraine symptom.
This is a summary of the clinical implications of these findings:
“The diminishing opioid analgesic efficacy during a course of opioid therapy is often considered as a sign of pharmacological opioid tolerance. As such, an opioid dose escalation has been a common approach to restoring opioid analgesic effects, assuming that there are no contraindications and no apparent disease progression. . . . [A]pparent opioid tolerance is not synonymous with pharmacological tolerance, which calls for opioid dose escalation, but may be the first sign of opioid-induced pain sensitivity suggesting a need for opioid dose reduction.”
While I firmly believe that pain sufferers should have access to opioids, the issue is much more complicated than DEA intervention. They’re an easy scapegoat and a problem for sure, but the body’s roadblocks may be a greater obstacle. Perhaps we should listen to our bodies and not rely so heavily on opioid pain relief.
While I was writhing in pain last week, sure that someone had covered my pillow with thumbtacks, I distracted myself by thinking about allodynia. I’d like to say that I considered the physiology of it, but I really just repeated the word mentally, thinking about how neat it sounds. Allodynia, allodynia, allodynia. It rolls right off the tongue.
About three-quarters of people with migraine have allodynia, which is the increased skin sensitivity that can feel like your hair hurts or that your jewelry is pressing into your skin. Basically, your nerves and brain become overly sensitive during a migraine. An hour or two before allodynia begins, other senses, like sight, hearing and smell, are also more keen because nerves are in a heightened state. Research indicates that migraine abortives are most effective if taken before skin sensitivity begins. If you’re interested in learning more about this phenomenon, see the ACHE article on central sensitization.
See, even silly distractions can be useful. Allodynia, allodynia, allodynia. . .