Mechanism of Action of Spa Therapy in Fibromyalgi

The mechanisms by which immersion in mineral or thermal water or the application of mud alleviates chronic pain and the symptoms of FS are not completely known. The net benefit is probably the result of a combination of factors, among which, mechanical, thermal, and chemical effects are most prominent.^18–20 A distinction can be made between the non-specific (hydrotherapeutic in a broad sense) mechanisms of simple bathing in hot tap water, and the specific (hydromineral and crenotherapeutic) mechanisms, which depend on the chemical and physical properties of the water used. Whereas the former are well known, the latter are difficult to identify and assess. Buoyancy, immersion, resistance, and temperature all play important roles. Hot stimuli produces analgesia on nerve endings by increasing the pain threshold. It causes relief of muscle spasms through the gamma fibers of muscle spindles and activates the descending pain inhibitory system. According to the “gate theory”, pain relief may be due to the temperature and hydrostatic pressure of water on the skin.³⁰

Spa therapy provokes a series of endocrine reactions, particularly in the release of adrenocorticotropic hormone (ACTH), cortisol, prolactin and growth hormone (GH), although it does not alter the circadian rhythm of these hormones.³¹ A dysregulation of the HPA axis, marked by mild hypocortisolemia and glucocorticoid feedback resistance, has been demonstrated in FS patients.^32,33 These findings can explain the beneficial clinical effects of spa therapy in FS.

Furthermore, various spa therapy techniques have been demonstrated to increase plasma levels of beta-endorphin.^34,35 Interestingly, it has been found that application of mature thermal mud in healthy individuals brings about a rapid increase in plasma beta-endorphin, which returns to pretreatment levels within the period of the so-called thermal reaction.³⁶ This increase in beta-endorphin explains the analgesic and anti-spastic effect of spa therapy, which is particularly important in patients with FS and is one of the key factors in the mechanism of individual tolerance to thermal mud baths.

A recent study has shown a reduction in circulating levels of IL-1, PGE₂ and LTB₄, important mediators of inflammation and pain, in FS patients undergoing a cycle of balneotherapy.²⁷ It has been suggested that inflammatory process mediated by cytokines, proteases, and inflammatory mediators located in the soft body tissue may play a role in the pathogenesis of FS, in up to one third of FS patients.³⁷ This inflammatory process would stimulate subcutaneous nociceptors, resulting in a sensation of pain. The detection of IL-1, IL-6, and tumor necrosis factor-? (TNF-?) in the skin of one-third of FS patients, and elevated plasma PGE₂ levels in FS support this hypothesis.³⁸ In another study of the same authors, it was demonstrated that reduction in masseter PGE₂ level after intramuscular glucocorticoid administration was associated with a decrease in resting pain.³⁹ The inhibitory effect of balneotherapy on the production and/or release of IL-1, PGE₂ and LTB₄ could explain the mechanism of clinical benefits of spa therapy in this disorder. Mineral water also may influence the oxidant-antioxidant system, which could be beneficial, because oxidative stress disorders have been described in FS.^40,41 In fact, in patients with FS, Bagis et al⁴² demonstrated an increase of serum malondialdehyde (MAD) and a decrease of serum superoxide dismutase (SOD), which support the hypothesis that FS is related to an imbalance of oxidant/antioxidant system.

Finally, other factors may contribute positively to the beneficial effects of spa therapy in FS, such as change of environment, the “spa-scenery”, the absence of (house) work duties, physical and mental relaxation, the non-competitive atmosphere with similarly suffering companions, and physical therapy.^18–20 As such, spa benefits could perhaps be attributed also to the effects of factors unrelated to the “water” therapy per se. These spa benefits are especially important in studies evaluating the effects of balneotherapy compared with no treatment or another treatment.

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