Traditional and Evidence-Based Acupuncture in Headache Management: Theory,
Mechanism, and Practice

Posted 07/07/2005
Chong-hao Zhao, MD, PhD, DABMA; Mark J. Stillman, MD; Todd D. Rozen, MD
Abstract and IntroductionAbstract
Acupuncture, traditional Chinese needle therapy, has become widely used for the
relief of headache. The history of the practice of acupuncture in the United
States and the theoretical framework for acupuncture in Chinese medicine are
reviewed. The basic scientific background and clinical application of
acupuncture in the headache management are discussed.
Introduction
About one million of American patients receive alternative medicine treatment,
an estimated 10 millions visits each year.[1] In response to this growth, many
US medical schools have created alternative medicine curricula and begun to form
academic departments of alternative medicine.[2]

Acupuncture, probably the most celebrated example of alternative medicine, is an
important therapy in China, Japan, and Korea. In recent years, with the growth
of interest in alternative medicine, acupuncture has become more popular in the
United States as a treatment option. Despite the fact that more scientific
studies are needed to confirm the efficacy of acupuncture, the National
Institutes of Health Consensus Development Panel (NIHCDP) issued a report in
November 1997 stating "acupuncture may be useful as an adjunct treatment or an
acceptable alternative or be included in a comprehensive management program."[3]
This statement will be discussed below.

There are an estimated 10 000 acupuncturists in the United States, including
approximately 3000 physician acupuncturists.[1] The practice of acupuncture is
regulated by individual states,[2] whose medical boards disseminate clear
guidelines for education and certification of physicians. For those licensed
physicians who are interested in obtaining board certification as DABMA
(Diplomate, American Board of Medical Acupuncture), the American Academy of
Medical Acupuncture requires 200 hours of didactic and clinical training as a
prerequisite for taking the board exam. Both passing the board exam and clinical
experience of at least 500 medical acupuncture treatments are required for the
application of diplomat status in the American Board of Medical Acupuncture.[4]
Nonphysicians can be trained in acupuncture in 16 schools accredited by the US
Government to give 4-year courses in acupuncture or oriental medicine.[2]

To western thinking, it is difficult to understand how acupuncture relieves
headache by placing needles in the scalp and neck, or, by treating points in the
hands and feet. This essay briefly reviews the historical and theoretical
framework for acupuncture, the scientific evidence for its mechanism, efficacy
in headache relief, safety profile, and potential difficulty in the clinical
acupuncture research.
History
Acupuncture is thought to have existed in China in one form or another since at
least the Xia Dynasty (2000 to 1500 BC).[5] It was first recorded in 1800 BC in
The Yellow Emperor's Classic of Internal Medicine.[6] Acupuncture was first
brought to Europe in the 1700s and was introduced to the United States during
the 19th to 20th centuries. Sir William Osler recommended acupuncture for the
treatment of acute lumbago in his classic medical textbook.[7] In the 1950s
China reported the use of electroacupuncture (EA) to obtain surgical
analgesia.[1] In 1972, the National Institutes of Health gave its first grant to
study acupuncture.[8] In 1973, an NIH acupuncture conference in Bethesda,
Maryland concluded that "Acupuncture holds some promise as an anesthetic for
certain surgical operations and for the treatment of some acute and chronic
painful conditions."[9] However, two recent events have brought special
attention to acupuncture for medical use. In 1996, the United States Food and
Drug Administration changed the classification of acupuncture needles from
Class III (experimental) medical devices to Class II (nonexperimental but
regulated) medical devices.[10] Being Class III hindered standard use of
acupuncture, as acupuncture could only be performed in approved research
settings (eg, hospital laboratories).

In November 1997, the National Institute of Health (NIH) established a consensus
development panel to evaluate the efficacy of acupuncture for treatment of
different disorders.[3] A bibliography of 2302 references was provided to the
panel and a conference audience of 1200. Twenty-five experts from different
specialties presented data with relevant citations to the panel and the
audiences. While many studies have demonstrated the potential of acupuncture,
few of the studies meet the high quality of contemporary research standards. The
review panel found equivocal results in different studies, poor design, small
sample size, and the inadequate selection of placebo controls. Because many of
the studies used nonneedling controls, it is difficult to interpret whether the
outcome reflects true acupuncture efficacy or just placebo needling effect.
Thereafter, NIHCDP evaluated the efficacy of acupuncture based on the "needling"
effect reported in the literature and cautiously concluded that
acupuncture may be efficacious in treating the adult postoperative and
chemotherapy nausea and vomiting, postoperative dental pain; useful as an
adjunct treatment or an alternative in treating addiction, stroke
rehabilitation, headache, menstrual cramps, tennis elbow, fibromyalgia,
myofascial pain, osteoarthritis, low back pain, carpal tunnel syndrome, and
asthma; and that it be included in a comprehensive management program. In order
to continue to examine the potential of acupuncture as a useful therapeutic
option for various conditions, the NIHCDP recommended further high-quality
controlled trials. More details about acupuncture research will be discussed
below.


Theory of Acupuncture in Traditional Chinese Medicine
From the Chinese perspective, acupuncture is necessarily embedded in a complex
theoretical framework that provides conceptual and therapeutic directions. The
theories of Yin and Yang, five elements (the evolutionary phases of fire, earth,
metal, wood, and water), Qi (vital energy) and blood, meridians (acupuncture
channels) and acupoints, provide the most important guidance for acupuncture
treatment. These theories will be described very briefly below, interested
readers may obtain detail explanation from the relevant textbooks.[5,11,12]

Firstly, Yin and Yang theory is among the most important principles underlying
the practice of all the Chinese medicine. The concept of Yin and Yang is the
generalization of the two opposite aspects in related objects and phenomena in
the natural world. The Chinese believe that all the objects in the universe
include the two opposite aspects of Yin and Yang. Some Yin-Yang examples include
tranquility and motion, lower and upper body, parasympathetic and sympathetic
system, meridians correlated with designated Yin (Zang) and Yang (Fu) organs
(described below).[11] According to the concepts of the Chinese Medicine,
disease and pain are the result of imbalance of the Yin and Yang, and
acupuncture treatment aims to restore that balance.[11,12] Secondarily, Qi and
blood is another pair of important concepts in Chinese Medicine. The ancient
Chinese believed that Qi is the vital energy or life force, and all that matters
in the universe appears by the movements and mutations of Qi.[11]
According to traditional tenets and beliefs, Qi circulates inside the meridians
and supports every life process and every organic function. Qi and blood
circulate and function together; that Qi is the major force driving the blood
circulating in the vessels.[11,12] If Qi flows, the blood will move; if Qi
stops, the blood will stop. Pain is the result of stasis or blockade of the
meridian Qi flow and the subsequent blood stagnation. Thirdly, the internal
organs, in Chinese medicine, are divided into two categories: Zang and Fu. Zang
organs include heart, liver, spleen, lung, and kidney. Zang organs function to
transform and store the essential Qi. Fu organs include gallbladder, stomach,
large intestinal, small intestinal, bladder, and triple energizer. Their major
function is to digest the food and excrete the waste. As in other fields of
medicine, the diagnosis of Yin and Yang conditions of Zang-Fu organs can be
accomplished by a detailed history inquiry, physical exam including
pulse palpation and tongue inspection. Fourthly, concepts of Jing and Luo are
important for acupuncture practice. The Jing-Lou meridian network consists of
major meridians (Jin channels) and minor meridians (Luo collaterals). Jing-Luo
meridians are distributed throughout the body and inside the meridians Qi flows
continuously. There are 14 major meridians, including 12 "regular" and 2
"curious" meridians in the body.[13,14] They are named according to their
distributed organs: lung, pericardium, heart, large intestine, triple energizer,
small intestine, stomach, gallbladder, bladder, spleen, liver, and kidney. The
abbreviation and alphabetic code endorsed by the World Health Organization (WHO)
for these meridians are LU, PC, HT, LI, TE, SI, ST, GB, BL, SP, LR, and KI,
respectively.[15] The two major curious meridians, include the conception vessel
(Renmai, CV) and governor vessel (Dumai, GV), locating at the midline of the
head and trunk in the front and back, respectively.
Acupuncture points are the sites through which the Qi of the organs is
transported to the body surface via the above described meridians. The
acupuncture points are divided into three categories: acupoints of 14 regular
meridians, extraordinary points, and Ashi points. (1) Acupoints of 14 regular
meridians are the major components of the acupoint system. (2) The extraordinary
points locate in parts of the meridian network other than the 14 regular
meridians. They are an important complement to the regular acupoint system and
contribute to pain management. (3) Ashi points are also called tender points.
They do not have specific names and defined locations, and they are highly
important in the diagnosis and treatment of headache and pain. Lastly, the
theory of five elements holds that all the objects and phenomenon in the
universe are formed or derived from wood, fire, earth, metal, and water, each of
which is designated specific characteristics. For example, wood represents
objects
or phenomenon with bending and straightening nature.[5,11,16] There exist
creative and controlling interactions among these five elements and a paradigm
including these five elements represents a model of acupuncture widely used in
the Western countries, including the United States.[5,16,17] The treatment
examples of this paradigm are described in reference books and are beyond the
scope of this article.[16,17]

Scientific Basis
Despite some preliminary experimental evidence supporting acupuncture's
analgesic effect on the trigeminocervical complex either directly or indirectly,
the exact mechanism remains unclear.
Histological and Physiological Characteristics of Acupoints
One of the most controversial issues in the acupuncture treatment is whether
needling the specific acupoints achieves better therapeutic effect than needling
any point (ie, a point not recognized as an acupoint).[3] Histology and anatomy
of acupoints have been studied.[18,19] They are in the vicinity of the small or
large peripheral nerves and their bifurcations, neuromuscular attachments, blood
vessels, ligaments, and suture lines of the skull.[18,19] Dung further found
that all the acupoints in the face and forehead region are located along
terminal or cutaneous branches of the trigeminal nerve and between muscular
branches of the facial nerve.[20] Langevin and colleagues recently found an 80%
correspondence between the sites of acupoints and the location of intermuscular
or intramuscular connective tissue planes in postmortem tissue sections.[21]
They also found that needling the true acupoints would penetrate different
tissue structures compared to the nonacupoints.
Histologically, needling true acupoints will penetrate first dermis and
subcutaneous tissue, then deeper fascia or interstitial connective tissue. In
contrast, needling the nonacupoints will penetrate the dermis, subcutaneous
tissue, and reach the muscle and bone, less likely passing through or inserting
into the deep fascia layer. Passing through the deep fascia connective tissue
layer may provide an effect on the tissue known as "winding around the needle."
It is not known exactly how this phenomenon affects the acupuncture treatment
outcome. Experienced acupuncturists often find that manually rotating the needle
will generate a local resistance around the needle that can be easily felt.[21]
Researchers have found that this resistance is at least partially due to the
traction on surrounding tissues.[22] The winding phenomenon is visible on
ultrasonic imaging and results in the "grasp force" that prevents the needle
from being pulled out.[21] Using the computer-controlled needling
instrument, a quantitative study found that the pull-out force in the acupoints
is 18% significantly greater than at nonacupoints 2 cm away.[23] More traction
or resistance occurs in the subcutaneous tissue and deep fascia of acupoints
than at the nonacupoints (subcutaneous tissue only).[21] The winding phenomenon
between the needle rotation and tissue whorl may lead to development of sensory
signals via mechanotransduction.[24] This serves as one of the hypotheses
explaining the distinction between true acupuncture versus placebo needling.[21]
It is postulated that mechanical signals arising from acupoint stimulation can
induce an effect including gene expression, protein synthesis, bio-physiological
change, and extracellular matrix modification. The lasting modification of
extracellular matrix surrounding the needle may in turn influence the other
structures sharing this connective tissue matrix, such as sensory afferents,
fibroblasts, immune, and vascular cells.[21] Therefore,
needling the acupoints (vs. nonacupoints) will more likely create mechanical
signals and subsequent bio-physiological effect. Several studies were done to
observe the difference of physical property between acupoints and
nonacupoints.[25-27] In Johansson's study, acupoints were first marked on the
skin and the control points were then marked 3 mm away of each of them. The
temperature and electrical resistance for each point were measured and analyzed
statistically. The acupoints had significantly higher local skin temperature and
lower skin electrical resistance, compared to control points. A later study by
Hyvarinen indicated that the diameter of the low-resistance skin points ranged
from 1.0 to 2.0 mm, and the distribution of these points resembled that of the
classical acupoints.[27] Increased skin conductivity was also reported in the
acupoints in rats and men, compared to the nonacupoints.[26] It is still unclear
what contributes to the difference of skin electrical properties.
Based on the distinction of skin electrical resistance and conductivity,
diagnostic and therapeutic probes have been developed. Such probes can help the
acupuncturists or researchers to locate the acupoints by detecting the fall of
cutaneous electrical resistance of the patients,[28] and even be used for
treatment of those points. Stimulation to the classical acupoints might achieve
stronger analgesic effect, compared to the nonacupoints.[29]
Inhibitory Effect of Acupuncture on the Trigeminal Nucleus Caudalis and the
Dorsal Horn
The trigeminal nucleus caudalis (TNC) is the site of synaptic interaction
between the first- and second-order nociceptive neurons. The TNC receives the
trigeminal afferent pain signals from the cranial vessels and dura mater.[30]
C-fos expression, a measurement of neuronal activity in the TNC, can be
increased by stimulation of the superior sagittal sinus or by administration of
substances (ie, nitric oxide agonist glyceryl trinitrate, 5-HT2B agonist
m-chlorophenylpiperazine) known to induce the migraine.[31-33] Drugs known to
abort the migraine, such as sumatriptan and valproate, reduce c-fos expression
in the TNC.[31,34,35] Some experimental studies have demonstrated the
suppressive effect of acupuncture on the TNC, as measured by c-fos
immunoreactivity. Using animal models, EA to the acupoint Neiting (ST 44) was
found to suppress the increased c-fos protein expression evoked by the tooth
pulp stimulation (TPS)[36]; EA also suppressed the jaw opening reflex response
to TPS or
direct stimulation of the TNC in rat,[37,38] and the suppressive effect could
be aborted by transection of the spinal trigeminal nucleus at the level of the
obex.[38] Furthermore, EA also inhibited the evoked potential in TNC following
the TPS.[39-41] The inhibitory effect of acupuncture on the TNC may be at least
partially mediated by the suppression of substance P (SP) release locally. In
the study from Takagi and Yonehara,[42] the potential in TNC evoked by TPS was
coupled with the increased release of local SP. EA suppressed both the evoked
potential and release of SP in TNC, and this inhibitory effect was significantly
antagonized by the pretreatment of naloxone or methysergide. This suggests that
EA's effect on the TNC, including the release of SP, may involve the modulation
from serotoninergic and opioidergic systems. The TNC projects the trigeminal
signal to various part of the rostral brain structures, including rostral
trigeminal nucleus, nucleus solitary tract, reticular
formation, thalamus, hypothalamus, ipsilateral cerebellum, limbic system,
cingular cortex, insular cortex, and auditory/visual association area.[43] In
turn, it receives the central inhibitory modulation from many structures
including the rostral trigeminal nucleus, nucleus raphe magnus (NRM), dorsal
raphe nucleus, periaqueductal gray area (PAG), rostral ventromedial medulla
(RVM), locus ceruleus, parabrachial area, the insular cortex, hypothalamus, and
somatosensory cortex.[43-45] There is experimental evidence demonstrating that
acupuncture may be able to activate some of these TNC inhibitory structures. EA
to the acupoint Quanliao (SI18) increased the c-fos protein expression in dorsal
raphe nucleus, the locus ceruleus, the hypothalamus, the thalamus, the RVM in
rat[46]; EA to the acupoint ST44 not only suppressed the increased c-fos protein
expression in the TNC response to TPS, but also activated the c-fos protein
expression in the PAG.[36] Using the electrophysiological
technique, EA to the acupoint Zusanli (ST36) was found to increase the firing
of the "excitatory" neurons in the NRM which, in turn, exerted the descending
inhibition of the nociceptive response to noxious stimulation of the tail skin
in the rat.[47] These neurons are likely serotoninergic in nature.[47,48] In
addition, the acupuncture's effect on the TNC may be influenced by the secondary
somatosensory cortex. In the study by Reshetniak et al[49] the evoked potential
of TNC induced by the TPS was inhibited by EA, and this inhibitory effect was
decreased after the functional inactivation of the secondary somatosensory
cortex.
Central Modulation of Acupuncture on the Spinal Dorsal Horn Neuron
Stimulation of the superior sagittal sinus in the cat and monkey increases the
c-fos activity in TNC and dorsal horns (DHs) at C1 and C2 levels.[32,50] The C1
and C2 cervical DH are considered to be the caudal functional extension of the
TNC, and implicated in the migraine pathophysiology.[51] Most studies of
acupuncture's effect on the spinal DH are nonspecific and often focus on the
entire spinal cord. While the specific effect on the upper cervical neurons is
still unknown, a review of its effect on DH neurons may give us a hint to help
to understand the potential mechanism. Data from animal studies suggest that
acupuncture may directly suppress nociceptive response of the spinal DH neurons.
In the anesthetized dog model, EA increased the level of immunoreactive
met-enkephalin in the cervical spinal cord and medulla.[52] The enhanced
immunoreactivity of enkephalin in the spinal cord was correlated with increased
pain threshold.[53] In addition, the expression of proenkephalin
(precursor of enkephalin) mRNA in the spinal cord was also enhanced, suggesting
increased biosynthesis of this precursor in the spinal cord.[54] Lee and
colleague demonstrated that the increased c-fos expression in the spinal DH
induced by noxious stimulation was inhibited by the EA, and this effect, in
turn, could be reversed by naloxone.[55] In addition, acupuncture may be able to
influence the DH cells indirectly by several mechanisms. Firstly, some studies
have demonstrated that acupuncture may presynaptically inhibit the afferent pain
transmission in the DH.[56-61] This may be mediated through a gate control
mechanism via stimulation of A-beta fibers.[61] This inhibition associates with
the increased release of enkephalin from the enkephalinergic interneurons in the
spinal cord during the acupuncture.[52] The enkephalin binds to opiate receptors
at the endings of nociceptive primary afferents, suppresses the release of SP
from these terminals, and results in a block of pain
transmission.[62] Secondly, acupuncture may activate rostral brain structures
that send descending inhibition to the DH neurons.[47,54,63-66] Neurons in the
NRM project descending serotoninergic inhibitory pathway to the DH cells in the
substantia gelatinosa.[47,48] The NRM receives input from the PAG which is
modulated by the hypothalamus and amygdala.[48] EA has been found to increase
the mu binding sites in PAG, NRM, hypothalamus, and amygdala,[67] stimulating
the release of beta-endorphin in the CSF and plasma.[66] Destruction or removal
of the major sources of beta-endorphin-the hypothalamus and the
pituitary-abolishes the analgesia resulting from EA,[64,68] suggesting that the
analgesia of EA is in part mediated by the hypothalamus-pituitary-PAG-NRM
descending inhibitory system. This pathway is also implicated in the central
inhibition of the trigeminal nociception and may play a role in the migraine
pathogenesis.[43] Besides the possible activation of NRM serotoninergic
descending inhibition to the spinal DH neurons, acupuncture may also activate
structures that send the descending noradrenergic inhibitory pathway to the
spinal DH neurons. Noradrenergic neurons in the reticularis
paragigantocellularis lateralis (RPGL) in the medulla project a descending
noradrenergic inhibitory pathway to the spinal cord.[65] Stimulation of RPGL in
rat by EA increases the pain threshold, implicating the activation this
antinociceptive system.[65] The major source of norepinephrine, the pontine
locus ceruleus is activated by EA, with resultant increased c-fos expression in
this location.[45]
Peripheral Modulation of Acupuncture
Some cervical acupoints are very important and are frequently included in the
treatment formula of both research studies and clinical treatment of migraine,
tension-type headache, and cluster headache.[29,69-71] Needling these points
likely alters the function of upper cervical neurons. For example, acupoints
Fengchi (GB20) and Tianzhu (BL10) have long been documented in acupuncture
textbooks[12,16] for headache treatment and are frequently mentioned in
acupuncture studies of different kinds of treatments of headache.[29,70,71]
Anatomically, needling these two acupoints will pass through the local skin and
muscles innervated by C2-5,[72] effecting nociceptive input in the corresponding
myotomes and dermatomes.
Inhibitory Effect of Acupuncture on the Pain Processing in the Headache Patients
Several studies have demonstrated that acupuncture stimulates the change in some
pain modulating substances in the headache patients. Nappi et al observed the
temporarily but significantly higher increase in plasma opioid levels in the
chronic post-traumatic headache patients after 5 minutes of acupuncture
stimulation.[73] Another placebo-controlled study on 22 pediatric patients with
migraine demonstrated that true acupuncture stimulated increased activity of
opioidergic system including the increased release of beta-endorphin in the
plasma. This was coupled with clinical improvement.[74] Low CSF met-enkephalin
levels in cluster headache were elevated by acupuncture.[75] However, the
relationship between CSF met-enkephalin and cluster headache is still unknown.
Serum magnesium levels were also increased with acupuncture treatment of
migraine, coupled with the clinical improvement.[76] Intracellular magnesium is
considered an antagonist of NMDA (N-Methyl-D-aspartate)-receptor[77] and
this receptor is linked to the development of central sensitization of
second-order neurons.[43] Ionized magnesium deficiency has been implicated in
the pathogenesis of migraine and tension-type headache.[78-80]

In summary, acupuncture (especially EA) has demonstrated the potential of direct
or indirect inhibition of TNC and DH neurons. This effect may be modulated by
several pain neurotransmitters and peptides.





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