RESUMO
Background/Objective: Obesity, characterized by chronic inflammation, may serve as a surrogate marker for more dysfunctional peripheral inflammation, potentially exacerbating FM symptomatology. Given this premise, this study aimed to investigate the effects of obesity as an effect modifier on neural and clinical variables, specifically those indexing pain-compensatory mechanisms in FM symptoms. Methods: A cross-sectional study was conducted with 108 participants who underwent a standardized TMS protocol assessment to measure resting motor threshold (MT), intracortical facilitation (ICF), and intracortical inhibition (ICI). Clinical data were collected using Beck's Depression Index (BDI), PROMIS, the Brief Pain Inventory (BPI), and conditioned pain modulation (CPM). Linear regression models were used to explore the relationship between these variables while examining Body Mass Index (BMI) as a potential effect modifier. If it was found to be a modifier, we stratified the sample into two groups with a BMI cutoff of 30 and performed another regression model within the subgroups. Results: BMI was identified as an effect modifier in the relationships between ICI and BDI, PROMIS fatigue, and CPM and in MT versus CPM. After stratification, non-obese fibromyalgia subjects demonstrated significant correlations between clinical symptoms and CPM and ICI activity. However, these correlations were absent in the obese group, suggesting obesity disrupts pain mechanisms and their compensatory effects. Higher MT values were associated with weaker endogenous pain control, particularly evident in the obese group. Conclusions: Obesity appears to be a significant effect modifier and delineates two patient groups across multiple clinical and neural assessments of fibromyalgia. Additionally, it suggests a role for obesity in exacerbating fibromyalgia symptoms and disrupting physiological pain-inhibitory mechanisms.
RESUMO
BACKGROUND: The multifaceted nature of Fibromyalgia syndrome (FM) symptoms has been explored through clusters analysis. OBJECTIVE: To synthesize the cluster research on FM (variables, methods, patient subgroups, and evaluation metrics). METHODS: We performed a systematic review following the PRISMA recommendations. Independent searches were performed on PubMed, Embase, Web of Science, and Cochrane Central, employing the terms "fibromyalgia" and "cluster analysis". We included studies dated to January 2024, using the cluster analysis to assess any physical, psychological, clinical, or biomedical variables in FM subjects, and descriptively synthesized the studies in terms of design, cluster method, and resulting patient profiles. RESULTS: We included 39 studies. Most with a cross-sectional design aiming to classify subsets based on the severity, adjustment, symptomatic manifestations, psychological profiles, and response to treatment, based on demographic and clinical variables. Two to four different profiles were found according to the levels of severity and adjustment to FMS. According to symptom manifestation, two to three clusters described the predominance of pain versus fatigue, and thermal pain sensitivity (less versus more sensitive). Other clusters revealed profiles of personality (pathological versus non-pathological) and psychological vulnerability (suicidal ideation). Additionally, studies identified different responses to treatment (pharmacological and multimodal). CONCLUSION: Several profiles exist within FMS population, which point out to the need for specific treatment options given the different profiles and an efficient allocation of healthcare resources. We notice a need towards more objective measures, and the validation of the cluster results. Further research might investigate some of the assumptions of these findings, which are further discussed in this paper.