Whole-Body Cryostimulation in Fibromyalgia: A Scoping Review

: Currently, all available therapies for the control and management of ﬁbromyalgia (FM) are mostly focused on relieving patients’ symptoms and improving their quality of life. The purpose of this review is to provide an up-to-date overview of the evidence supporting the beneﬁcial effects of whole-body cryostimulation (WBC) in patients with FM and evidence-based guidance on the possible adjuvant use of WBC in the treatment of FM. We searched the most recent literature by retrieving 10 eligible studies, 4 of which were abstracts only, from a total of 263 records. Thermal stress caused by cryostimulation induces an analgesic effect, improving pain, redox balance, and inﬂammatory symptoms in an exercise-mimicking fashion. In addition, it reduces the feeling of fatigue, improves mood, and reduces mental health deterioration with positive consequences on depressive states and improved sleep quality. Although the studies included in this review are not of sufﬁcient quality and quantity to draw deﬁnitive conclusions about the effectiveness of WBC in FM, initial evidence indicates WBC as a promising add-on option in the multidisciplinary treatment of FM, due to its rapid action and high patients’ compliance. The application of WBC protocols has the potential to expand therapeutic options for the treatment of FM and related disorders; however, larger, high-quality primary studies are still needed.


Introduction
Fibromyalgia (FM) is a medical condition characterized by the combination of complex, sometimes indistinct, symptoms. FM manifestations include chronic widespread musculoskeletal pain and associated fatigue, morning stiffness, sleep disturbances [1,2], depression, anxiety, and cognitive symptoms [3,4], in line with the biopsychosocial model of pain [5], and evidence related to other chronic pain conditions [6][7][8]. In addition, FM is associated with psychological factors, such as neuroticism [9], alexithymia [10], catastrophizing [11], and low health-related quality of life [4], limiting people's daily activities as well as their social, professional, and recreational activities [12,13]. FM is the third most common musculoskeletal condition and is estimated to affect 0.2 to 6.6% of the adult general western population [14,15]. Due to its persistent and debilitating condition, FM imposes enormous economic burdens on society, as patients with FM have relatively high levels of comorbidities and high levels of health care utilization and cost [16].
Despite predisposing factors (genetic, stressful or traumatic events, viral infections, and obesity), the etiopathogenesis of FM is still not fully unraveled, making its diagnostic and classification criteria confusing. One of the most widely held hypotheses regarding a compensatory mechanism, downregulation of blood pressure [50], even overnight [51], may result in reduced feelings of fatigue, improved mood, and reduced mental health deterioration with possible positive consequences on depressive states, and improved sleep quality [43]. Recent literature has shown that WBC is immunostimulating and yields an anti-inflammatory response, with a decrease of the pro-inflammatory cytokines and increases of anti-inflammatory mediators [52][53][54][55][56][57]. It also appears to improve the effect on redox balance in a session/treatment number-, age-, and fitness-dependent manner [58], probably through the decrease in the total oxidant production which, consequently, induces antioxidant activity [56,[58][59][60][61][62][63]. Thus, due to its widely recognized anti-inflammatory, antioxidant, analgesic, and exercise-mimicking effects [64], WBC is proposed as a promising add-on option in the multidisciplinary treatment of FM, considering also that diffuse inflammation is one of the sub mechanisms of depression [65], and that co-morbid depression is very common among FM patients, with a lifetime prevalence of 62-86% [66]. In addition, all the articles we have cited in this scoping review reported no major side effects even after a great number of WBC sessions demonstrating the possibility of developing protocols that include a large number of treatments. This scoping review aims to update the reader as to the current evidence supporting the therapeutic effects of WBC in patients with FM and directions on the possible adjuvant use of WBC in the treatment of FM.

Materials and Methods
All the procedures of this scoping review followed an unpublished review protocol which was drafted prior to the electronic search. This search was conducted using the electronic databases Pubmed, Scopus, Embase and Web of Science using strings that combined keywords referring to WBC with keywords referring to FM. Figure 1 illustrates the flowchart of the literature search, while the complete strings and number of records retrieved in each database are given in the Supplementary Materials (Table S1). No restrictions were applied regarding the publication date, and only articles written in English, Italian, French, and Spanish languages were considered. The reference lists of the existing reviews focusing on cryotherapy were scanned to find further relevant records. The studies were included if: (1) they were published in an original article or as conference proceedings, (2) they evaluated the effects of WBC, defined as short exposures to air temperatures below −100 • C, and (3) their study sample was composed by patients with an age between 25 and 70 and with a medical diagnosis of FM. The lists of the records retrieved by performing the electronic search were uploaded to the online software Rayyan [67] to perform the title and abstract screening. Three independent reviewers performed this screening and conflicts were resolved by consensus. Then, the full texts of the screened articles were assessed and the ones that met the inclusion criteria and did not meet the exclusion criteria were included in the review. This assessment phase was performed by two reviewers and conflicts were solved by consensus. A pre-specified spreadsheet was used to extract data from the included articles. The following data were extracted: study design; country where the study was performed; experimental population and experimental subgroups (including drop-outs); age (means and standard deviations or median and interquartile ranges); female percentage of the sample; WBC protocol (and other therapy protocols, if used, such as mud bath and hot air) including number of WBC sessions, duration of each WBC sessions, and WBC temperature; sampling (measurements, surveys) time; primary and secondary outcome(s); outcome assessment instrument(s); and synthesis of the results. A Downs and Black modified checklist [68,69] was used to evaluate the methodological quality of evidence under the categories of reporting, external validity, internal validity-bias, internal validity-confidence (selection bias), and power. The Downs and Black quality assessment tool was modified by removing questions about interventions performed because some studies included in this review used observational study designs. This quality evaluation instrument consisted of four sections that assessed the quality of reported outcomes (items 1, 2, 3, 6, 7, 9, and 10), external validity (items 11 and 12), internal validity (16, 17, 18, 20, and 26), and power (item 27). The highest score for the item was 25, with a higher total score Appl. Sci. 2022, 12, 4794 4 of 18 indicating higher quality of evidence for the specific study. Quality and level of evidence were assessed by two authors (JMF) and (MG), and is summarized in Table 1 It was not used to evaluate studies in abstract-only format due to their obvious low score as a result of the inability to address most of the checklist questions. The Downs and Black modified checklists assess the following domains in both randomized and non-randomized studies: quality of the reporting, external validity, presence of bias, presence of confounding, and power of the applied statistical analysis. The extracted data were tabulated to provide a description of each study and the results were described narratively.
modified by removing questions about interventions performed because some stud included in this review used observational study designs. This quality evaluat instrument consisted of four sections that assessed the quality of reported outcomes (ite 1, 2, 3, 6, 7, 9, and 10), external validity (items 11 and 12), internal validity (16, 17, 18, and 26), and power (item 27). The highest score for the item was 25, with a higher to score indicating higher quality of evidence for the specific study. Quality and level evidence were assessed by two authors (JMF) and (MG), and is summarized in Table  was not used to evaluate studies in abstract-only format due to their obvious low score a result of the inability to address most of the checklist questions. The Downs and Bla modified checklists assess the following domains in both randomized and no randomized studies: quality of the reporting, external validity, presence of bias, presen of confounding, and power of the applied statistical analysis. The extracted data w tabulated to provide a description of each study and the results were describ narratively.

Results
The database search retrieved 263 records in total, and 10 of the returned articles, which includes original articles and conference abstracts between 2000 and 2018, with a total of 597 participants (446 with primary fibromyalgia, 21 with rheumatoid arthritis, 20 with chronic low back pain, 13 with ankylosing spondylitis, 11 with osteoarthritis, 4 with secondary fibromyalgia, and 2 with other autoimmune diseases), met eligibility criteria and were included in this review. Table S1 illustrates the search strings employed during the electronic search and the number of records retrieved, Table 1 summarizes the quality and level of evidence of the selected articles, Table 2 presents their characteristics and Table 3 summarizes their outcomes and results. Two articles used a non-controlled study design [31,36], three articles used a non-randomized controlled study design [33,37,38], five articles used a randomized controlled study design [32,34,35,39], and one of them used a crossover design [40]. Five studies were conducted in Germany [31,32,[36][37][38], two in Italy [33,34], and one each in India [39], Spain [40], and Belgium [35].
Scoring the quality of the articles using the Downs and Black modified quality checklist was carried out independently by three researchers (MG, JMF, and PP), who discussed their scoring disagreements and reached a consensus. The maximum score that articles could receive from this assessment tool was 14 out of 15 points. The average score was 11.6 points. No articles reached the maximum score of 15. The quality assessment of each of the included articles is presented in Table 2. As mentioned above, evaluation of the quality of conference abstracts [31,32,34,39] was not included due to the different type of format that would have influenced the evaluation. Pain intensity, condition, state, or level was evaluated in eight studies [32][33][34][35][36][37][38]40]. Four studies assessed physical and mental health [33,35,39,40] while only one assessed global health status [33]. Three studies assessed fatigue [33,34,39], and well-being [36], number of tender points [38], sleep disturbances [39], and quality of life [35] were each assessed by only one study. Severity of FM [39] and disease activity [40] were evaluated in one study each. Two studies quantified the changes in gene expression: one using transcriptomics [60] and analyzing transcripts fold change, the other study quantifying the change of gene expression in specifically selected genes (CCL4, TGFBR3, CD69, and MAP2k3) [31]. Finally, only one study investigated the markers of inflammation IL-1, IL-6, IL-10, and TNF-α [37]. Each study considered recruiting of patients diagnosed with FM. One study also included patients with rheumatoid arthritis, chronic low back pain, ankylosing spondylitis, osteoarthritis, secondary fibromyalgia, and other autoimmune diseases [36]. All articles compared the effects of WBC on FM, at baseline and after more than one exposure. Eight articles used only one experimental group (FM patients) [31][32][33][34][35][38][39][40], while, as mentioned above, one paper included other diseases besides FM [36]. Of note, healthy controls exposed to WBC were used only in one occasion [37]. One article also compared the effect of WBC to the effect of warm therapy (consisting of a warm mud bath followed by hot air) [38]. Two articles performed a follow-up of one [35] and three [37] months respectively. All studies included more than 50% female subjects.
In six studies using WBC, the participants spent a 10-sec-to-1-min adaptation period at −60 • C in a vestibule connected directly to the main chamber [31][32][33][34]38,40]. Afterward, cryostimulation was applied at −110 • C in four studies, −140 • C in two studies, and −105 • C, −130 • C, and −196 • C in one study each. One study did not state the temperature [39]. The cryostimulation treatments lasted between two and three minutes in every study. The number of exposures varied between 3 and 48 sessions. A cryosauna was used in two cases [37,40], and a cryochamber in the eight other studies. Among the adverse effects during and after cryotherapy included: heartbeat feeling in whole body, palpitations, sleep difficulties, bowel sounds and bloating, muscle stiffness, tremor, headache [40] or migraine, burns (comparable to a light sunburn), increase in pain, shortness of breath, feeling of anxiety due to the narrowness of the chamber, circulatory problems, dizziness, and anxiety [36] and anxiety symptoms, partly with panic attacks [38].

Discussion
This literature review includes original articles and conference abstracts between 2000 and 2018 describing the effects of WBC in patients with FM and aims to provide a comprehensive and up-to-date summary of the most recent findings supporting its adjuvant therapeutic use. Given the paucity of good quality published studies on this topic, a systematic review could not be conducted. This exploratory review primarily describes and discusses the effects of WBC on pain (intensity, level, changes and impact, and painful tender points); impact of disease (ability to perform large muscle tasks, difficulty with work, pain, fatigue, morning tiredness, stiffness, and depression); severity of FM (prevalent clinical manifestations, emotional, physical, and coping [active and passive] aspects); selfrated physical mental and global health; emotional (anxiety and depression) and physical factors (pain, fatigue, sleep quality, and functional ability); well-being index; health-related quality of life; hematological inflammatory parameters; gene expression of protein involved in inflammatory, pain processing pathways and small nucleolar RNAs.

Clinical Effects of WBC in FM
Pain perception involves interconnected physiological and psychological mechanisms that include anatomical, physiological, cognitive, and affective components of pain [70]. There are two neural pathways that regulate pain signals: ascending pathways that transmit sensory signals through peripheral nerves, including nociceptive signals, to the spine and brain for processing; and descending pathways that send modulatory (excitatory and/or inhibitory) signals from the brain to the periphery, regulating ascending nociceptive signals that reach the brain [71]. These physical and noxious chemical signals are detected by nociceptors, specialized receptors in peripheral nerves activated by physical stimuli (i.e., changes in temperature, pressure, and impact). Many neurotransmitters and neurochemicals are involved in the transmission of pain signals such as norepinephrine and serotonin [72].
In FM, these two neural pathways operate abnormally causing an increased activity in the pain matrix which results in central amplification of pain signals, a phenomenon named central sensitization [73]. Several studies of FM-related pain and hyperalgesia have demonstrated the involvement of spinal mechanisms and an enhanced response to somatic and cutaneous stimuli throughout the brain's pain matrix, allodynia and hyperalgesia. In most cases, patients become hypersensitive to pain. The constant hypervigilance to pain can also be associated with psychological problems [74].
Most of the studies included in this review (7 out of 10) hypothesized that WBC should alleviate pain and/or inflammatory processes in FM patients, with the aim of improving health-related quality of life. These studies tested the therapeutic efficacy of WBC and its practicability for clinical routine in FM, also comparing it to other therapies (warm therapy or steam therapy) or treatments (antioxidants and analgesic agents).
All studies reported an analgesic effect of WBC with significant reduction in pain level, but had different settings. Bettoni et al. carried out two studies on the efficacy and safety of WBC in FM patients. The first report showed the superiority of WBC compared to antioxidants and analgesic agents, in terms of pain and fatigue reduction [34]. In the second study, patients performed aerobic exercise (cycle ergometer or treadmill) for 30 min immediately after WBC [33]. Physical activity, which is also used to treat FM, may have masked these results by opposing its induced vasodilation to WBC-induced vasoconstriction. In the cross-over trial of Rivera et al., the individuals' VAS and FIQ scores did not return to baseline after the first treatment with WBC due to too short washout periods, so that only results of the first sequence could be reported [40]. Vitenet et al. reported that WBC significantly improved health-reported quality of life, evaluated through the changes in the Medical Outcome Study Short Form-36 (10 sessions over 8 days) [35]. However, the sample size was limited, as only 11 patients underwent WBC and the control group protocol was not described in detail. This was the same for the study of Metzger et al. that described a decreased pain intensity and a short-term pain relief of about 1.5 h after cold application. No control group receiving a regular rehabilitation program could be compared to a group additionally treated with WBC [36]. Therefore, the reduction in pain could probably be due not only to the analgesic effect of the WBC, but also to the effect of the applications carried out in parallel. However, they described some adjustment time before reaching maximum pain relief, in their case after about two weeks (half of the treatment). Interestingly, most patients rated the effect of WBC as not very effective in the context of the overall treatment, perhaps also due to the session conditions (temperature −105 • C and 2-3 patients in the chamber). Klemm et al. included patients with standard treatment before and during the study, excluding physical activity as a possible confounder of the reduced level of pain found after WBC treatment, but no control group not undergoing WBC was present [37].
Only Rivera et al. [40] and Klemm et al. [37] investigated the effects of WBC on FIQ, and only Vitenet et al. [35] and Klemm et al. [37] included a follow-up, after 1 and 3 months, respectively, showing that the effects of WBC on pain and disease activity after discontinued treatment were no longer reduced. In addition, Klemm et al. demonstrated that serial WBC (between 6 and 10 sessions in a maximum of 3 weeks) elicited effects for more than 1 month after the end of WBC treatment, then decreasing gradually to null effect after 3 months [37].
Two studies compared the effects of WBC with other classic thermotherapy methods. Kurzeja et al. investigated the effect of thermotherapy with WBC (−110 • C) alone compared with mud bath (+40 • C) and hot air (+42 • C) combined in the daily shift. Pain intensity was reduced in all groups with no significant differences between groups [38]. However, the pain scores in the WBC group were lower and the patients described a 2-h pain relief after cold exposure.
The abstract of Sundaram mentions that WBC provides better results in association with physiotherapy than with steam therapy. Improvement in pain, general health, fatigue, and sleep are attributed by the author to the systemic response and serotonin levels stimulated by WBC [39]. However, no information about the temperature was mentioned, the sample was not homogeneous in terms of age and gender, and there were no actual data to corroborate the findings and conclusions.

Molecular Effects of WBC in FM
The pathogenesis of FM not only includes pain sensitivity, pain inhibition, or pain amplification, but also an imbalance of pro-and anti-inflammatory cytokines, genetic predisposition, and environmental triggers such as mechanical/physical trauma or injury and psychosocial stressors that ultimately leads to pain and impaired pain processing.
There is growing evidence of neuroinflammation in FM. Several pro-inflammatory cytokines, including TNF-α, IL-1β, IL-6, and tumor necrosis factor α (TNF-α), have been found to be elevated in animal models of neuropathic pain and in the cerebrospinal fluid (CSF), peripheral tissues, and blood of patients with chronic neuropathic pain conditions [75]. In addition, pharmacologically lowering or blocking of these pro-inflammatory cytokines has been demonstrated to prevent, reduce, or reverse pain (allodynia and hyperalgesia) in both animal models and clinical studies [76].
Thus, the imbalance of pro-and anti-inflammatory cytokines is assumed to play a role in the induction and maintenance of pain and the occurrence of many of the clinical features of FM (such as swelling, dysesthesia, skin manifestations, fluid retention, and increased levels of fibronectin, which is a tissue marker of endothelial activation) as a result of a neuroinflammatory condition that gives rise to descending pathways that influence predominant symptoms, such as pain, fatigue, and cognitive impairment. In addition, environmental triggers, stress, and emotions are the upstream driving mechanism of neurogenic inflammation in FM [77].
Therefore, the likelihood that FM may have an imbalance in cytokine production and secretion has been confirmed. Ucelyer et al. showed that FM patients have higher serum levels of IL-1ra, IL-6, and IL-8, and higher plasma levels of IL-8, compared to controls [78], while two studies of Lubkowska et al. showed how WBC affects the inflammatory status by inducing an imbalance towards the anti-inflammatory side [55,56]. Consecutive sessions of cryotherapy increased levels of IL-6, which can act both as a pro-inflammatory and anti-inflammatory cytokine, and IL-10, an anti-inflammatory cytokine, and lowered the IL-1α levels. Furthermore, WBC appears to improve the oxidative status already after a limited number of sessions, in a dose-dependent way [58,59].
Klemm et al. integrated the clinical effects with the molecular effects of WBC [37]. In parallel with changes in disease activity and pain reduction, patients with FM showed a significantly different response to WBC compared with healthy controls in terms of changes in IL1, -6, -10, and TNF-α over time to WBCs. FM patients had higher levels of IL-1, -6, -10, and TNF-α at baseline compared to healthy subjects. IL-1, IL-6, and IL-10 levels decreased significantly after three and six sessions and stabilized up to three months after discontinued WBC treatment. Interestingly, IL-6 levels returned to baseline after three months only in healthy controls and showed significantly decreased IL-6 levels at each reading point compared to baseline. WBC had no effect on TNF-α levels, neither in FM patients nor in healthy controls.
Therefore, even if the levels of IL-1, IL-6, and IL-10 in FM patients were higher than healthy controls after 6 WBC sessions and 3 months after the last WBC session, their significant alteration confirms the overall beneficial effects of WBC.

Gene Expression after WBC in FM
Drynda et al. investigated the changes in gene expression on peripheral blood cells of patients with FM going through a series of three exposures to WBC within three days [32]. One study correlated the reduced pain intensity with transcripts that were found significantly changed already after a single exposure to WBC. The majority of down-regulated transcripts belonged to a group of small nucleolar RNA (SNORD) while the up-regulated transcripts were a few specific genes, such as PBX1, SFRP2, MAP2K3, and SLC25A39. SNORD molecules belong to so-called non-coding RNAs. Emerging evidence has demonstrated that they are involved in various physiological and pathological cellular processes acting as internal signals that control various levels of gene expression. However, the sample size and homogeneity were rather limited, as only 10 patients were studied.
Another study from the same group investigated on a larger cohort of 22 patients the changes in the gene expression of selected genes (CCL4, TGFBR3, CD69, and MAP2K3) identified as significantly regulated in cells from peripheral blood of patients with FM going through a series of three exposures to WBC within three days [31]. The expression levels of CCL4 and CD69, two proteins produced upon activation of T-lymphocytes, reduced significantly after the third exposure compared to baseline. In contrast, the expression of MAP2K3, a protein activated by cytokines and environmental stress in vivo, was found to be up-regulated in 13 patients, while the expression levels in the other 9 patients remained almost unchanged. Interestingly, the changes of gene expression were evident already after the first cold exposure, but reached statistical significance after the third exposure. The down-regulation of TGFBR3, a membrane proteoglycan that often functions as a co-receptor with other TGF-β receptors observed in the pilot study, could not be confirmed in the larger cohort. Unfortunately, both studies are scientific abstracts only and do not provide further speculation or discussion of the results.

Conclusions
Our scoping review summarizes the current understanding of the role of WBC as an adjunctive treatment for FM. The article has several limitations. First, the molecular mechanisms and regulation of gene expression behind the reported beneficial effects of WBC have not been fully investigated, as only changes in a few inflammatory markers and genes have been observed. Second, the absence of standard protocols for the use of WBC in the treatment of FM (temperature, number of sessions, exposure time, and sample collection time) might be responsible for the inconsistency of the reported results. In this regard, many of the studies we evaluated had confounding factors such as physical activity and pharmacological treatment, which play a key role in the modulation of several pain components (such as anti-inflammatory and antioxidants). Third, the lack of adequately designed randomized controlled trials, a blinding system, or adequate control groups within the researched papers substantially reduced the quality of the articles. In general, the modest amount of published literature, the low quality of the studies and information provided, the absence of standard protocols, and the small irregular sample sizes make it difficult to compare results between studies. Randomized control trials are needed to confirm and strengthen the significance of WBC-induced clinical changes and identify its effects at the molecular level. Therefore, the results of our scoping review cannot definitively support WBC as an effective adjunctive treatment for FM. However, despite important limitations of the available studies, initial evidence indicates that WBC reduces FM symptoms. Particularly due to its rapid anti-inflammatory effect, WBC has the potential to improve rehabilitation programs in patients with FM, which seems attractive in terms of the cost-effectiveness of rehabilitation. Not secondarily, the high patient compliance and highly positive perception of treatment reported in most studies seem to make WBC a preferred component of the rehabilitation program, which appears crucial in the long-term management of FM.