Mechanism of Action
Perhaps the most puzzling aspect of acupuncture to both the lay person and physician with a knowledge of anatomy, neuroanatomy, and physiology is how an unmedicated needle, inserted at a site remote from its desired application can work, eg, a point on the lower leg affecting gastric function, or a point on the hand affecting headache.
Skeptics maintain that acupuncture has basically a placebo effect, since the acupuncture meridians and their energy or chi (Qi) as described in TCM cannot be directly observed, dissected, or measured with standard anatomic approaches or physiologic instrumentation. The acupoints are located at sites that have a high density of neurovascular structures and are generally between or at the edges of muscle groups. These locations, curiously, are less painful than random needle sticks into a muscle group. An interesting study demonstrating the map of a meridian pathway involved the injection of Technitium99, a radioactive tracer, into both true and sham acupoints. The scan of the injection sites showed random diffusion of the tracer around the sham point but rapid progression of the tracer along the meridian at a rate that was inconsistent with either lymphatic/vascular flow or nerve conduction. Another study demonstrated that needling a point on the lower leg traditionally associated with the eye activated the occipital cortex of the brain as detected by functional magnetic resonance imaging.
Opium addicts who underwent acupuncture analgesia for surgery were noted not to go through narcotic withdrawal compared with similar patients who received conventional anesthesia. This gave birth to the endorphin hypothesis, which has been explored as one of the mechanisms of action of acupuncture. Needling affects cerebrospinal fluid levels of endorphin and enkephalin, and such effects can be blocked by the opiate antagonist naloxone. A number of other imputed mechanisms of action have used the model of the acupuncture needle as an electrode, which activates changes in the ionic milieu of the interstitial fluid, these changes being rapidly conducted along the fascial lamellar planes by the highly conductive electrolyte medium. Because nociceptive stimulation, such as with a transcutaneous electrical nerve stimulation unit, is known to block pain perception, the neurogate theory has also been suggested as a mechanism of action for acupuncture.
The presence of a foreign body (the needle) may act to stimulate vascular and immunomodulatory factors, including locally occurring mediators of inflammation. Measurements of adrenocorticotropic hormone (ACTH) have been demonstrated to be elevated after acupuncture treatments, suggesting that adrenal activation and release of endogenous corticosteroids may also result from acupuncture. Various physics concepts such as quantum physics, electromagnetic force field changes, and wave phenomena have been proffered to explain the nonlocal effects of acupuncture.[9,10]
Explanation of the TCM system of medicine, including the effects of acupuncture, is rich with metaphor and allegory. Such explanations refer to different kinds of Qi, the influence and interaction of the five elements (fire, earth, metal, water, and wood), yin and yang, and other terminology that requires contemplation and long study of a culturally distinct system. It is a model so different from the standard medical model that we advise Western-trained physicians and students to hold a temporary suspension of disbelief to nonjudgmentally approach learning about it as a system of medicine, and, if interested, to review the topic in more depth in some of the references listed.[2,3,5,10] It is probably best to tell patients, students, and colleagues, in answer to the question of how acupuncture works, that the conclusive answer is yet to be determined, though research has given us some windows of insight into possible mechanisms of action.[5,8,9,10,12,13,14]
South Med J. 2005;98(3):330-337. © 2005 Lippincott Williams & Wilkins
Cite this: Acupuncture: A Clinical Review - Medscape - Mar 01, 2005.