To the best of our knowledge, this is the first study to analyze the predictors of poor improvement in symptom severity at the end, and three months after completion, of eight-session cycle of acupuncture treatment in FM patients. The results of this study can provide a reference, from the perspective of PPPM/3PM, for the integration of a non-drug treatment such as acupuncture into the complex FM scenario. The identification of predictors at two different time points, namely at the end of the treatment course (T1) and after three months (T2), may provide useful information to know what to expect in the immediate and near future.
Specifically, a high number of tender points and high levels of pain magnification at the end of treatment, and concomitant duloxetine therapy, 3 months after the end of the acupuncture cycle, respectively, were identified as the main predictors of significant non-response to acupuncture.
Nowadays, the widespread prevalence of chronic non-communicable diseases results in an important global socio-economic burden. In these chronic conditions, of which FM is a part, the use of PPPM/3PM strategies is crucial to achieve better outcomes [24]. Though FM to date is not a preventable disease, something can be done in tertiary prevention, seeking treatments that are effective, well tolerated, and not harmful to patients. Acupuncture meets these characteristics; however, there is some variability in efficacy in patients with FM and therefore it is highly desirable to be able to identify patients with low probability of response.
Acupuncture for fibromyalgia in the PPPM/3PM framework
The need to identify predictive risk factors for a given disease is especially critical for those non-communicable conditions with high prevalence, for which the implementation of simple and inexpensive biomarkers would be welcome [25, 26]. For these conditions, which include those characterized by chronic pain, it is also very important to identify predictive variables of response (or non-response) to treatment.
Acupuncture, with its history dating back thousands of years, has a body of evidence for efficacy in the area of chronic pain and FM [8, 27], which, however, is predominantly derived from a reactive medical approach. For example, a 2008 study showed the efficacy of acupuncture in addition to usual care (exercise and tricyclic anti-depressants), but without studying the predictor variables of efficacy itself [28]. Subsequent studies, although well conducted and adhering to the rules of randomized controlled trials, were always characterized by the absence of analysis of predictive variables of efficacy so that individualized treatment could be carried out and therapeutic failure prevented [29, 30].
This study aimed to demonstrate that acupuncture can be a therapeutic intervention embedded in the broader horizon of PPPM/3PM. The role of acupuncture in personalized medicine is beginning to be studied in multiple disciplines, first of which is oncology [31]. Being able to predict treatment response is one of the cornerstones of precision medicine. On the other hand, response to a given treatment is a complex phenomenon, depending on genetically determined factors, biomarkers, and also on measurable clinical and psychosocial characteristics [32].
Stratification of patients with FM based on genetic characteristics or biomarkers is still far from being applicable to clinical practice. Therefore, the present study focused on identifying clinical predictive variables that can be easily measured and applied to daily practice.
Predictors of non-response
The shift to personalized medicine is increasingly based on data derived from biobanks, for FM biobanking is still not widely used [33, 34]; the approach remains purely clinical.
Interestingly, clinical features that represent the diagnostic/classifying definition of FM in the latest ACR and AAPT criteria sets [13, 35, 36], namely chronic widespread pain (in this study assessed through the SAPS), fatigue, and non-restorative sleep, were not identified as predictive variables. It is also interesting to note that while chronic widespread pain was not predictive of treatment response, TPC predicted immediate response to acupuncture. Though TPC has been basically abandoned for diagnostic/classification purposes by the most recent criterion sets, its assessment may represent a measure of distress and be more informative than dolorimetry [20].
Pain catastrophizing has been shown to be related to tenderness and affective distress in patients with FM and rheumatic diseases [37]. Pain catastrophizing, particularly in terms of pain magnification, is associated with a decreased response to acupuncture based on the results of this study. A functional magnetic resonance imaging study demonstrated how the tendency to pain catastrophizing interferes with neural mechanisms involved in pain processing. In patients with high pain catastrophizing, increased brain activity has been detected in the bilateral dorsolateral prefrontal cortex. This kind of patients would appear to be less easily distracted by pain, and thus pain catastrophizing would seem to be a feature strongly associated with the persistence of chronic pain [38]. In a previous study, it was shown that among the various scales of the PCS, magnification is the one that does not experience significant improvement with acupuncture compared with helplessness and rumination [10]. Therefore, magnification is a psychological trait that does not only yield to substantial improvement with acupuncture, but also predicts its lack of efficacy in the immediate future, and patients with high magnification should probably be directed to other therapeutic approaches.
The relationship between concomitant duloxetine treatment and lower chance of improvement three months after the end of acupuncture treatment is probably less intuitive. A possible explanation involves the pharmacodynamics of duloxetine and the mechanisms of action of acupuncture. Duloxetine is a dual serotonin and norepinephrine reuptake inhibitor. Acupuncture in chronic pain exerts multiple effects peripherally and centrally involving multiple mediators. Numerous studies conducted in the animal models, show that serotonin and norepinephrine are two pivotal neurotransmitters in the effect of acupuncture with actions at both the encephalic (e.g., raphe magnus, locus coeruleus) and spinal levels [39]. One hypothesis that can be advanced is that some of the effect of acupuncture overlaps with pathways that are already pharmacologically elicited. However, this remains a theoretical speculation that needs experimental verification.
Study limitations
The main potential limitation of the study is the absence of a control group with sham acupuncture. It was chosen to treat all patients with verum acupuncture due to symptom severity since the latter has been shown to be more effective than sham interventions in patients with FM [40]. In addition, there is some direction in the literature suggesting the execution of pragmatic real-life studies since acupuncture is a complex therapy and sham procedures have been shown to be non-inert and potentially, rather than reducing bias, may introduce additional ones [41, 42].