Does moxibustion work? An overview of systematic reviews

Background Several systematic reviews (SRs) have assessed the effectiveness of moxibustion for a range of conditions, often with contradictory conclusions. Our aim was to provide a critical evaluation and summary of these data. Methods Electronic searches were conducted to locate all SRs of moxibustion for any condition. Data were extracted by two authors according to predefined criteria. Results Ten SRs met our inclusion criteria, which related to the following conditions: cancer, ulcerative colitis, stroke rehabilitation, constipation, hypertension, pain conditions and breech presentation. Their conclusions were contradictory in several instances. Relatively clear evidence emerged to suggest that moxibustion is effective for breech presentation. Conclusions Based on evidence from the currently available SRs, the effectiveness of moxibustion has been demonstrated for several conditions; however, due to the poor quality of the primary studies, there remains considerable uncertainty.


Background
Moxibustion is an East Asian therapeutic method that uses the heat generated by burning herbal preparations containing Artemisia vulgaris to stimulate acupuncture points [1]. According to the theory of traditional medicine, heat is usually applied to acupuncture points during moxibustion to cure diseases by regulating the function of meridians and visceral organs. A possible explanation for how moxibustion works is that the heat stimulates acupuncture points, which increases qi circulation and relieves qi stagnation, leading to an improved disease state [2].
Acupuncture stimulation, which involves thrusting or twisting needles, results in various biochemical reactions that can have effects throughout the body. Unlike acupuncture, moxibustion uses heat stimulation at various temperature levels, ranging from mild skin warming to tissue damage from burning. This heat stimulation can yield inflammatory responses and induce vascular changes [2].
Although moxibustion is often used as a symptomatic treatment for a wide range of conditions in clinical practice, e.g., arthritis, gastrointestinal problems, gynaecological complaints and stroke rehabilitation, its clinical effectiveness remains uncertain [3][4][5], and many experts doubt its biological plausibility. Numerous clinical trials have emerged; however, their results are contradictory. Thus, SRs assessing the summary of this evidence may bring clarification. To date, several such articles have been published. Unfortunately, however, the conclusions drawn in these publications are also conflicting.
This overview is aimed at summarising and critically evaluating all SRs on moxibustion as a symptomatic treatment for any condition. Our ultimate goal is to provide clinicians with clearer guidance regarding the value of this therapy.

Methods
The following databases were searched on July 22, 2010 without language restrictions: Medline, EMBASE, AMED, CINHAL, the Cochrane Library, six Korean Medical Databases (Korean Studies Information, DBPIA, Korea Institute of Science and Technology Information, Korea Education and Research Information Service, KoreaMed and Korean National Assembly Library) and Chinese Databases (CNKI). In addition, our extensive departmental files were searched by hand. The keywords used in the search were (systematic review OR meta-analysis) AND (moxa OR moxibustion). Articles were included if they related to a formal SR or meta-analysis on any type of moxibustion as a treatment for any type of condition. Reviews, comments and overviews without a systematic methods section were excluded.
To be included, the SR had to be concerned specifically with the effectiveness of moxibustion and include evidence from at least two controlled clinical trials. SRs evaluating moxibustion together with acupuncture without separate evaluation of each approach were excluded.
Key data were extracted independently by two authors (MSL & JWK) according to predefined criteria, including conditions, number of primary studies, methodological quality of the primary studies, conclusion of each SR, and data related with searching. Disagreements were resolved by discussion between the authors. Judgement about the quality of the primary studies was adopted from the respective SRs. The Overview Quality Assessment Questionnaire (OQAQ) was used to evaluate the methodological quality of all included SRs [6]. In the OQAQ, the score ranges from 1 to 7. A score of 3 or less was considered as indicative of major flaws, whereas a score of 5 or more suggested only minor flaws. The two authors did these assessments independently, and discrepancies were settled by discussion.
For one particular condition, breech presentation, three SRs were available [7][8][9]. Two showed clearly positive results [8,9], whereas the other cast doubt on the clinical relevance of the effect due to the small number of included trials [7]. For the studies regarding cancer (10), stroke (11) and pain (12), the conclusions were cautiously positive. Equivocal conclusions emerged from the SRs on ulcerative colitis [10], constipation [14] and hypertension [15]. One SR evaluated the effects of moxibustion on various conditions and failed to arrive at a clearly positive conclusion [3].

Discussion
Our overview shows that several SRs on moxibustion have been published. The fact that most of them were recent indicates that the scientific interest in moxibustion is growing. Even though most of the reviews are of high quality [3,[7][8][9][10][11][12][13][14][15], they are based on few clinical trials that were not well controlled. Several SRs have arrived at positive overall conclusions; however, some of the studies regarding breech presentation contradict each other [7][8][9]. This can be explained by the time difference amongst the three SRs. The more up-to-date SR includes four to seven more rigorous and positive studies than the first SR [8,9]. Thus, the sum of the best evidence to date seems to suggest that moxibustion is effective for breech presentation.
Positive conclusions were also reached for the treatment for nausea and vomiting in cancer patients [11], stroke rehabilitation [12] and pain conditions [13].  Unfortunately, these SRs were based mostly on poor quality primary studies. Thus, considerable uncertainty about the value of moxibustion for these indications persists.
Three SRs relating to ulcerative colitis [10], constipation [14] and hypertension [15] were of poor quality, and all relied on a small number of flawed studies. It therefore seems fair to say that the value of moxibustion is not well-documented for any of these conditions.
In essence, this means that the effectiveness of moxibustion is currently not well-documented for several conditions, which is in sharp contrast to the many claims made by the proponents of this therapeutic modality, including those practicing traditional Chinese medicine or complementary and alternative medicine.
SRs on moxibustion have stated their studies to be limited by the often poor quality of the primary data. Our analysis confirms this view. Many of the primary moxibustion trials originate from China (data not shown); Vickers et al. demonstrated that virtually 100% of Chinese acupuncture trials are positive [16], which seems to be equally applied to moxibustion, an acupuncture-like intervention. This casts considerable doubt on the reliability of these studies. Collectively, these facts limit the conclusiveness of SRs on moxibustion, thereby leaving a level of uncertainty. SRs have been criticised for being often unable to provide specific guidance. Yet, even if uncertainty prevails, SRs have the important function of mapping areas of doubt. Thus, as pointed out above, our overview highlights areas of research in which investment in further clinical trials would be fruitful.
Thus our overview of SRs suggests that future moxibusition-research should consider all necessary measure to minimize bias including development of possible sham or placebo moxibustion. We recommend to follow the CONSORT guidelines when designing clinical trials of moxibustion [17]. Similarly, SRs of moxibustion should abide by the PRISMA guidelines to reduce the risk of bias [18].
Our overview has several important limitations. Even though our search strategy was thorough, we cannot completely exclude the notion that relevant articles were missed. By evaluating systematic reviews rather than clinical trials, important details of the primary studies may have been lost. Most importantly, the poor quality of the primary data and the systematic reviews is regrettable. Collectively, these limitations limit the conclusiveness of our findings.
In conclusion, this overview of SRs suggests that moxibustion is effective for correcting breech presentation, whereas for other conditions, the evidence does not reach a firm conclusion because of several limitations. All SRs are, however, based on studies with a high risk of bias. Therefore, considerable uncertainty remains about the therapeutic value of moxibustion.