There have been no guidelines or recommendations for the therapeutic management of fibromyalgia until 2017. Therefore, the importance of the multidisciplinary approach is highlighted with special emphasis to non-pharmacological treatments as BT. Emerging evidence from prospective randomized trials has been reported with positive effects of BT on FMS. However, these studies have not reached conclusions with limited sample size and quality methods. Therefore, we performed an updated meta-analysis to determine the therapeutic benefits of BT in the management of FMS.
Naumann and Sadaghiani performed a meta-analysis on BT and hydrotherapy in FMS treatment, covering the literature up to April 2013. Ten RCTs were included, but only six of them with 321 participants were extracted and analyzed for their meta-analysis. They found moderate evidence of a medium-to-large effect on pain and TPC for BT, a medium effect on FIQ, and no significant effect on BDI.
Thereafter, there have been no latest systematic reviews regarding the topic during the past 6 years. our search identified valuable data from emerging RCTs. Notwithstanding the somewhat overlap of interested topic, our meta-analysis provided novel evidence to the vision of FMS treatment., whereas 10 studies with a total of 611 cases were included in our study. The updated three studies greatly expanded participants, which significantly improved the reliability of the meta-analysis results. Secondly, when we extracted and analyzed original data from included studies, we identified missing data from the previous meta-analysis . For example, Fioravanti et al  involved the follow-up of pain outcome, which was neglected in the previous study ; Moreover, VAS pain data for the endpoint follow-up were not included for pool analysis for two studies  in the previous meta-analysis. Nevertheless, the two studies provided VAS pain data at 3, 6, and 12 months after treatment. Only the data of sixth months of follow-up were included in the previous study . We extracted all informative data from original RCTs which may significantly improve the reliability of the meta-analysis results.
Our systematic review and meta-analysis with ten clinical trial studies, presented novel line of evidence that BT can benefit fibromyalgia syndrome with pain, FIQ, TPC at follow up. These findings are consistent with previous meta-analysis or reviews [10, 23]. However, there was no significant effect on BDI at follow up. Moderate evidence was found at the end of treatment to sustain these improvements. This outcome is contrary to the meta-analysis in 2014 and Evcik’s RCT in 2002 . However, our result is in line with Naumann’s when excluding ZIjlstra’s trials  reporting that mental health improvement was not as obvious as physical health, and the duration is short. In their opinions, there was only limited room for improvement of their study sample because of the low baseline levels of depression. Meanwhile, they have limited time in the spa, which is not a vacation. Therefore, the improvement in symptoms seems to be independent from absence of work duties . There was insufficient data on the side effects of BT, and no statistical analysis was performed.
There were three included studies adopting the 100-mm Visual Analog Scale [15, 16, 18]. Remaining studies used 10-mm Visual Analog Scale. Despite the dispency, a significant improvement of FMS-derived pain was noted. The degrees of pain relief vary among the included studies, with different baselines. There are additional basic therapies for FMS either BT group or control group, such as exercise, health education guideline and medicine. Existing evidence has not reached consensuses on differential effects of mineral water type on reducing pain among patients with FMS. Zijlstra et al. showed negative change in data indicating improvement of pain, especially at the third month of follow-up. However, it is not obvious at the end of treatment in control group. This findings was consistent with the results of Ardıç et al. It is possible that the function of BT in the elimination of inflammatory factors reached an extreme in a certain period of treat time . Beyond that time extreme, the pain relief from BT cannot continue. Therefore, other ways are needed to continue the effect.
Functional capacity in daily living activities were evaluated by FIQ.The results of our meta-analysis showed that BT can significantly improve the functional outcomes. Evcik et al. reported a better functional scores and quality of life in the bathing treatment group than that in the control group. Interestingly, the efficacy of the BT decreased with continuing of the treatment, although it was still effective in the last follow-up (24 weeks). However, this interesting finding was not observed in the Altan’s study. The possible reason for this interesting finding is that there is no subsequent treatment after the BT in Evcik’s study, which could not keep a persistent efficacy. Similarly, the current study found that TPC was significantly reduced in the bathing treatment group in comparison with the control group. This finding is also consistent with the previous studies [27, 28], which demonstrated that the BT has a significant effect on the improvement of TPC.
The efficacy of BT can be explained by heat, mineral content, and other physiologic and endocrine effects [29, 30]. Thermal stress stimulation exerts analgesic on nerve endings by increasing the pain threshold. It alleviates muscle spasms and activates pain-relieving inhibition system through the gamma fibers of muscle spindles. According to the “gate theory”, pain relief may be caused by water temperature and pressure on the skin [31, 32]. Physiologically, heat application leads to increased blood circulation, like BT，and heat application to inflamed tissue induces a reduction in circulating nociceptive elements; fresh oxygen introduced after free oxygen free radicals removal enhances the repair of the inflamatory tissue [33, 34]. In different musculoskeletal diseases, the effect of BT on pain and function is significantly better and longer than that of tap water bath at the same temperature . The minerals which are dissolved in the water play an important part in the mechanism of action of BT.
There is high heterogeneity (29% to 91%) for included studies. Firstly, there is clinical heterogeneity due to different in follow-up periods. It took 1 to 6 months to evaluate the results, although the average treatment intervention duration was about 2 weeks. The last follow-up time after interventional is an important factor in determining the sustained effectiveness of BT. Another relevant factor is that the composition of the mineral water is different. Also the exposure times and temperature used for BT. In addition, the ratio of female participants was higher in all studies. The pain threshold in men and women may be different. These factors may be connected with the differences between the groups, and affect the entire effectiveness and heterogeneity of the studies.
Several limitations of this meta-analysis should be recognized. Firstly, the included studies did not employ a unified evidence-based diagnostic system including mechanisms, common characteristics, comorbidities, and diagnostic criteria capable of improving the recognition of FM in clinical practice. Secondly, this meta-analysis includes ten publications, and in order to identify the factors leading to heterogeneity are still need additional studies to perform subgroup. Thirdly, each study had a different regimen, with spas in different areas.
In conclusion, our findings support the effectiveness of BT in pain control and functional improvement in FMS. The results that are gained from our study agree with the evidence of effectiveness of BT in controlling pain and improving functionality in FMS. In fact, spa therapy can be used as an effective backup of pharmacologic treatment of FMS and an effective alternative therapy for patients with drug intolerance. However, more powered randomized studies are needed to determine the results of meta-analysis.