Because of its multiple clinical manifestations, which range from musculoskeletal pain to complaints on other body systems and psychological disorders, multidisciplinary intervention has been recommended as the best approach for patients with fibromyalgia [23
]. The rationale for this intervention is that a sum of small gains can result in a significant improvement in the global functioning of these patients. Among the most recommended activities is cardiovascular training [24
], educative effort to support the understanding of the disease and pain controls strategies [25
] and pharmacological interventions with tricyclic antidepressants, selective serotonin reuptake inhibitors [26
] or weak opiates [27
]. The efficacy of multidisciplinary intervention to fibromyalgia has been demonstrated by different authors [23
]. Due to the interference of pain in multiple aspects of functioning in these patients, composite instruments which involve dimensions such as pain, sleep quality, functional capacity and emotional status are recommended to evaluate the results of this intervention [28
]. Parameters like HAQ, HDRS and BDI clearly improved, and FIQ showed a trend in the same direction, supporting the idea of global improvement in functional capacity, emotional aspects and reduction of the impact of fibromyalgia on functioning of these patients regardless the use of tDCS. These results on HAQ, HDRS and BDI reflect the beneficial effect of the multidisciplinary program both on psychological aspects and physical capacity, which result in an overall improvement of functioning.
Non-invasive brain stimulation has been proved to be effective for the reduction of pain in these patients in previous studies [9
], so we tested whether noninvasive brain stimulation with tDCS could enhance the effects of the multidisciplinary program in pain reduction. The rationale for using tDCS to enhance this multidisciplinary program is based on the mechanisms of these two interventions [29
]. The learning of new skills (in this case, reducing pain behaviors) is linked to changes in neuronal activity and excitability. They might reflect changes in synaptic strength, associated with long-term potentiation (LTP). Successful manipulation of cortical excitability to improve learning processes has been demonstrated in humans with tDCS [11
]. TDCS presents an interesting alternative to these approaches, because it is non-invasive, painless and safe (compared to drugs). In addition, tDCS modifies spontaneous neuronal activity and therefore can increase activity in a more physiological manner and in addition be used while training is being performed [4
]. Indeed several studies have shown that tDCS can increase cognitive gains when associated with behavioral interventions [4
The association of tDCS to the multidisciplinary intervention did not prove to be effective in reducing pain as measured by the VAS. However, the evaluation of pain according to the pain domain of SF-36 showed significant reduction only in the group that received active stimulation. These differences may result from some points that need to be discussed. First, the instrument of evaluation. VAS measurement of pain is related to the perception during the patient assessment. In this context, SF-36 is a more appropriate scale as it evaluates the previous 4-week period. Also, not only does this later instrument inquire about the amount of pain over the body in the last 4 weeks, but also to which extent it interferes with social life. Because the focus of multidisciplinary intervention was directed to behaviors, and not only pain perception, an instrument with broader range of observation, like social life participation, is more appropriated. This idea is supported by the trend toward a significant better improvement in quality of life according to the FIQ, which is also a multidimensional tool.
Another important aspect is that we performed weekly, rather than daily, sessions of tDCS and this strategy might be less effective according to a recent study in stroke subjects [30
], although this later study was directed to the treatment of depression, not pain. The rationale for weekly sessions was based on the fact that tDCS has shown to induce cumulative effects based on the findings of such use in chronic pain [8
] and depression [30
]. Therefore we hypothesized that stimulation once a week might induce cumulative effects. However the number of consecutive sessions to induce cumulative effects might be important as these studies used daily tDCS on weekdays for 10 sessions and showed some persistence of favorable outcomes on a 2 weeks follow-up. Stimulation of M1 was based firstly on the previous results of Fregni [9
], who proved it to be more effective than prefrontal stimulation. Also, it is hypothesized that the thalamus, and therefore rostrocaudal pain inhibitory neural pathways are stimulated by afferences from M1, resulting in reduction of pain perception [31
Because improvement with active tDCS was observed only in one of the chosen outcomes, our results failed to fully support our hypothesis that weekly tDCS combined with a multidisciplinary approach is associated with beneficial effects for fibromyalgia. Therefore it is not clear whether this scenario with some significant findings and other lack of significant results is because our strategy of treatment (weekly rather than daily sessions), type of intervention (multidisciplinary approach) or instruments of evaluation. This question needs to be further explored in studies using other strategies of treatment. Alternatively, weekly anodal stimulation with tDCS over M1 may add no value over conventional rehabilitation for fibromyalgia.
Another critical issue for our mixed results is our small sample size that was based on positive results from a similar study, but that had a different context (daily tDCS sessions and no multidisciplinary treatment). Therefore it is possible that we were underpowered to detect a difference in the active vs
sham groups in the other domains. Moreover, because both groups were under rehabilitation treatment, a reduction of effect size between stimulated and sham groups should be expected, requiring a larger sample to evidence the difference. However, we also considered that a significant difference with a larger population would not show a clinically meaningful result and in addition, in some of the tests, there was not even a trend for a significant result. Moreover, patient population was different as compared to Fregni’s study, in which patients did not undergo a simultaneous multidisciplinary approach [9
], and therefore might also explain the differences. Although it can be said that to many variables were involved in the intervention, like drugs, tDCS and multidisciplinary approach, it is important to remember that our object was to check the efficacy of the association of interventions, rather than each of them isolated. Because fibromyalgia is a chronic condition, a follow-up assessment would be desired, but this was not planned in this study. Another limitation of this study is the fact that multiple comparisons were performed without corrections, like Bonferrogni, so there in a possibility that the few positive finding are only due to chance. Finally the results of this study should be viewed as exploratory as to design further studies on this field.