In the case of acute and chronic pain associated with disorders of the musculoskeletal system, magnetotherapy is often applied as a safe and easy treatment method [29, 45]. Many studies have shown that the effectiveness of magnetotherapy is related to the nature of the magnetic field applied and the tissue sensitivity specific to the individual [2, 3, 29, 45]. Many authors, however, emphasise the lack of precise research protocols, parameters of magnetic field applied, and uniform assessment conditions [29, 31, 45–47].
The evidence reported by recent studies suggests that exogenous electromagnetic fields may be involved in many biological processes that are of great importance for therapeutic interventions [7, 26, 48]. Therefore, magnetotherapy has great potential to become a stand-alone treatment or adjunctive therapy for patients with musculoskeletal disorders. According to Tong et al. [52] it is still underestimated in the clinical practice [7, 49, 50].
In the case of patients with RA, due to the variety and extensiveness of the symptoms experienced by them, choosing the most effective and safe physiotherapeutic methods is still problematic [22]. Due to their non-invasiveness and deep tissue penetration, magnetic fields are often used in therapy [13, 23, 45].
In the present study, the assessment carried out after the rehabilitation program consisting of hand mobility exercise and 20-minute magnetotherapy sessions, showed a significant improvement in the functional status in the entire study group evaluated using HAQ-20 questionnaire, which is considered to be the most efficient method for assessing intervention outcome in patients with RA [42]. However, statistically significant improvement in HAQ-20 scores was only observed in PEMF Group. These results seem to be consistent with the findings reported by other authors who observed that treatments with a duration of 30 minutes or shorter produce more beneficial effects compared to treatments with longer duration [7, 51]. Similarly, authors of a literature review report that PEMF therapy improves the hand function in patients with degenerative joint disease [52].
The present study showed satisfying analgesic effects of the intervention in both SMF and PEMF Group. Other studies also reported that analgesic effectiveness of LF-PEMF therapies is higher compared to pharmacotherapy based on non-steroidal inflammatory drugs (NSAID) [53,54]. Furthermore, Shupak et al. showed that a single 30-minute PEMF therapy session reduced pain in RA patients, although the authors expressed doubts about the durability of the effects achieved after a single exposure [55]. Similarly, in a study by Kalmus et al. the use of SMF reduced pain in patients with rheumatic diseases. Additionally, the findings showed an improvement in sleep quality and a reduction in inflammation in patients receiving spa treatment [56]. In contrast, Dündar et al. reported greater analgesic effectiveness of shortwave diathermy and electrotherapy treatments compared to PEMF [57].
The current findings also show reduced duration of morning stiffness in SMF and PEMF groups. Likewise, a study by Kuliński & Skuza demonstrated that the duration of morning stiffness decreased from five to three hours in patients with Stage 3 and Stage 4 RA following physical therapy intervention, which included magnetotherapy. This effect, however, was only sustained for four months [18]. On the other hand, severity of morning stiffness in the current study was shown to decrease significantly in SMF group. Stolarzewicz & Szczuka also compared effects of static magnetic fields emitted by permanent magnets (SM), and low-frequency alternating magnetic fields (EM) on the severity of morning stiffness and found that the use of both EM and SM reduced severity of the problem [58]. It also appears that LF-PEMF therapy is more effective in reducing the severity of morning stiffness compared to high-frequency PEMF [52].
The present findings also show that the range of motion in the joints of both the dominant and the subordinate hand was improved in the entire study group, however the effect was better in PEMF Group. The lack of higher improvement in the range of motion in the subordinate hand in the entire group may be linked to the fact that the subordinate hand is less engaged in the activities of daily living and self-care. A similar study was conducted by Stolarzewicz & Szczuka who reported improved range of motion in the knee following both SM and EM therapy [58].
In the current study significant reduction in hand volume was only observed in PEMF Group. In contrast, Chen et al. evaluated the distant effects of SMF application at a dose of 35 mT (magnetic knee wrap) and found no reduction in joint effusion [59].
Despite numerous studies confirming the beneficial effects of magnetic fields, there were some concerns about the safety of this therapy when it was being introduced [60]. Subsequent observations showed that magnetic fields with flux density exceeding 10 mT can induce visual disturbances such as flashes or shape deformations [61]. The literature reviews available in bibliographic databases show that no negative side effects were reported in the participants of the studies conducted. In fact, the authors emphasise that magnetotherapy is well tolerated and can be a valuable adjunct to pharmacotherapy [4, 51].
At present researchers emphasise the occupational risks faced by physiotherapists and associated with exposure to low-frequency magnetic field emissions during treatments administered [50]. International standards issued by the World Health Organisation (WHO), and International Commission on Non-Ionizing Radiation Protection (ICNRP), permit environmental exposure to SMF with flux density of less than 40 mT, and less than 200 mT in the case of occupational exposure (8 hours per day) except for individuals with electronic and ferromagnetic implants [62, 63]. Safety of magnetotherapy procedures for both patients and the physiotherapists operating the magnetotherapy equipment require further study [9, 50].
According to the WHO, in the case of electromagnetic hypersensitivity (EHS), patients may experience various symptoms such as impaired concentration, sleep disturbances, excessive fatigue, dizziness, vomiting, palpitations, digestive disorders; non-specific dermatological symptoms: redness, tingling, burning; visual fatigue; increased sensitivity to chemical stimuli and other [62, 64]. Some researchers also mention side effects of SMF such as: headaches, nausea and vomiting and skin lesions [65, 66]. Furthermore, it has also been suggested that SMF may affect the course of neoplastic processes [67, 68]. Some authors emphasise that SMF with extremely high flux density in some cases may cause adverse health effects [69]. SMF with induction up to 8T was also found to adversely affect cardiovascular function, however these effects were within the range of normal physiological variability. Furthermore, even when flux density exceeding 2T was applied, some subjects reported dizziness and a metallic aftertaste in the mouth [70]. In fact Driessen et al. argue that SMF may produce side effect when the value of flux density is weak, up to one microTesla [47]. Both the WHO [62] and other authors [47] emphasise the methodological inadequacy and lack of precise magnetic field parameters in research investigating exposure of the living organism to SMF.
In the study by Thamsborg et al. side effects occurred in both the PEMF-treated group and the sham magnetotherapy group [71]. In that study there were no serious adverse effects leading to discontinuation of the treatments. Mild and transient side effects occurred during the first two weeks of treatment. Patients in both groups reported such symptoms as a grumbling or throbbing sensation, warming sensation, an aggravation of the osteoarthritic pain in the study knee [71]. According to this review, possible side effects after PEMF therapy may include joint pain, vomiting, increased blood pressure, numbness of peripheral parts of the body and paraesthesia of the feet, as well as cardiomyopathy [51]. Since side effects also occurred in the placebo-treated groups, the observations of the above authors [51, 71] do not allow a clear conclusion on the possible side effects of magnetotherapy.
Other researchers emphasise that LF-PEMF therapy can lead to lower blood pressure and slower heart rate [72]. In contrast, the authors of the review notice the lack of assessment of side effects in the studies discussed in the review [52]. Another important comment was contributed by Żurawski & Stryła who noticed that the duration of time between exposure to LF-PEMF and the beneficial as well as adverse effects of the therapy is not strictly defined [73].
The participants of the current study were affected by AR on average for 11.5 years and presented with Stage 2 and 3 functional changes, as well as Stage 2 and 3 radiological changes. According to Kuliński & Skuza effectiveness of rehabilitation is lower in patients with highly advanced RA [18]. Despite the fact that the patients presented with highly advanced RA, the current study found an improvement in all measured parameters. Nevertheless, the long-term effects of exposure to electromagnetic fields, both positive and negative, require further research [64].
LIMITATIONS
A possible limitation of this study is the lack of daily blood pressure measurements in specific patients and therefore it cannot be concluded definitively that patient-reported adverse effects were related to blood pressure fluctuations.
Another limitation is the fact that the duration of the disease was greatly varied in the study population. For ethical as well as organisational reasons (lack of consent of most patients to participate in the study if the rehabilitation programme was limited to kinesitherapy only), the authors were not able to create a control group, to be subjected only to kinesitherapy and no magnetotherapy. The study did not include a follow-up to assess long-term effects because the patients would have been required to refrain from any changes in medication applied or from using any other forms of therapy over the corresponding period of time.
Despite limitations we need to emphasise that the eligibility criteria for participants were strictly defined, as were the rigorous conditions for the magnetotherapy. All the patients participated in a uniform kinesiotherapy programme. A general assessment of the patients' condition (HAQ-20) was performed and a local, precise assessment of the hand was carried out.