You don’t want to experience pain, nor do your patients.
Unfortunately, the mainstream health care system is clearly failing those who suffer pain, particularly chronic pain (usually defined as daily pain lasting at least three months).
Most patients start with over-the-counter (OTC) pain remedies before turning to their regular doctor. This invariably leads to a revolving door of specialists, tests, diagnoses, and pharmacological treatments, none of which seem to provide much in the way of relief. Sadly, this story is all too common for far too many people.
Because of the far-reaching negative consequences of chronic pain, including effects on work, school and home life, it shouldn’t be surprising that patients are frustrated with the mainstream health care approach to pain management. Unfortunately, the standard model focuses on the symptoms of chronic pain, rather than trying to determine its root cause.
Research into gate-control theory, however, offers fascinating insight into the actual causes of chronic pain. Furthermore, understanding this theory can help researchers devise more effective treatments to combat pain.
The gatekeeper
For many years, pain perception was measured by the intensity and degree of tissue damage, regardless of patients’ prior experience with similar pain. In 1965, a landmark study was published forwarding the theory that there is a mechanism by which the nervous system acts as a gatekeeper to determine which pain signals to send to the brain. This was the beginning of what we now call gate-control theory to explain pain perception.1
According to gate-control theory, pain signals that are generated at a particular site of injury, such as the back or shoulder, do not go directly to the brain. Instead, there is a neurological gate inside the spinal cord that the pain signals encounter. This gate determines whether or not the signals will be passed to the brain.2
If this neurological gate is open, the pain signals are perceived by the brain as more intense. Conversely, if the gate remains closed, or only partially open, the pain is perceived as less intense.2,3
Gate control works through a combination of both thin- and large-diameter nerve fibers. Thin- diameter fibers carry information about pain, and large-diameter fibers transfer information about touch, pressure and vibration.2,3
This information is transmitted to two types of cells in the dorsal horn of the spinal cord: transmission cells, which pass the pain signal on to the brain; and inhibitory cells, which impede the activity of the transmission cells.
Activity from thin-diameter nerve fibers impedes inhibitory cells, allowing the transmission cells to fire and pass the pain signal along.
Conversely, activity from the large-diameter fibers activates the inhibitory cells, blocking or reducing the pain signal that is passed on to the brain.2,3
How the theory helps patients
While this description of the mechanism of pain seems highly theoretical, it directly explains why certain therapies can effectively provide relief, particularly the use of topical analgesics. As explained earlier, greater activity from large-diameter nerve fibers activates the inhibitory cells in the dorsal horn, thereby blocking pain signals. Given that these nerve fibers show greater response to touch, pressure and vibration, it seems clear that treatments that capitalize on these inhibitory responses will blunt pain signals.
An example of one such treatment is the application of topical analgesics, such as those that include menthol, camphor, lidocaine, salicylate, and capsaicin (either individually or
in combination), which have been shown to have many beneficial analgesic properties.4
Two recent studies appear to show promise for the use of topical analgesics that incorporate capsaicin. 5, 6
The first study, published in the European Journal of Pain, compared the single use of an 8 percent capsaicin patch to one dose of pregabalin for treating dynamic mechanical allodynia (DMA), a little-understood condition in which even a slight brush of the skin can cause a burning pain sensation.6
DMA is often associated with neuropathy. A total of 253 patients were assigned to either the capsaicin patch or pregabalin. Those patients using the patch reported greater reduction in affected area and intensity of DMA, as well as a greater proportion of complete DMA resolution. 5
The other study was published as part of the Cochrane Database of Systematic Reviews, which collects meta-analysis papers. These pool the results from a number of smaller papers on a given topic, aiming to discern patterns among the data.
This paper compared a variety of topical analgesics to treat both chronic and acute pain.6 In particular, the combined findings for treating post-herpetic neuralgia showed a moderate amount of evidence to support topical, high-concentration capsaicin treatment.5
Capsaicin has a number of benefits beyond OTC or prescription pain- killers, and poses no risk of dependence, addiction, or overdose. Combining a topical’s healing proper- ties with large-diameter nerve-fiber stimulation takes advantage of the gate-control mechanism to alleviate your patients’ pain with little to no risk of adverse side effects.
Tina Beychok is an editor and writer with expertise in technical, academic, and scientific materials. She is a regular contributor to Chiropractic Economics and resides in Long Beach, Calif. Her online portfolio can be viewed at thatwordgrrl.com, and she can be contacted at tbeychok@gmail.com.
References
1 Melzack R, Wall PD. Pain mechanisms: A new theory. Science. 1965;150(3699):971-979.2 Meldrum ML. “Pain.” Encyclopedia Britannica. https://www.britannica.com/ science/pain. Updated Nov. 2017. Accessed Jan. 2018.
3 Mendell LM. Constructing and decon- structing the gate theory of pain. Pain. 2014;155(2):210-216.
4 O’Neill J, Brock C, Olesen AE, et al. Unravelling the mystery of capsaicin: A tool to understand and treat pain. Pharmacological Reviews. 2012;64(4):939-971.
5 Cruccu G, Nurmikko TJ, Ernault E, et al. Superiority of capsaicin 8% patch versus oral pregabalin on dynamic mechanical allodynia in patients with peripheral neuropathic pain. Eur J Pain. 2017;doi: 10.1002/ejp.1155. [Epub ahead of print]
6 Derry S, Wiffen PJ, Kalso EA, et al. Topical analgesics for acute and chronic pain in adults- an overview of Cochrane Reviews. Cochrane Database Syst Rev. 2017;May 12(5):CD008609.
