Obesity as a Disruptor of the Pain Inhibition Response in Fibromyalgia: A Pooled Multi-Trial Analysis of 521 Patients

Background

BMI has been strongly associated with poor outcomes in fibromyalgia syndrome (FMS) patients, but no previous studies have examined its role in pain inhibition response. This study examines the influence of high BMI on the pain inhibition response and clinical severity of FMS.

Methods

This pooled cross-sectional analysis of baseline data from nine clinical trials involving 521 adult female FMS patients included the largest mechanistic FMS sample to date. Pain inhibition responses (conditioned pain modulation, CPM) were assessed using a computer-based thermode. Clinical assessments included numeric pain scales and Beck's Depression Inventory. Unadjusted and multivariate analyses were conducted to assess the influence of BMI on FMS symptoms using generalised linear models. Interaction terms for BMI and CPM were also tested. Non-linear effects of BMI were assessed with piecewise-linear models.

Results

A high body mass index (BMI) significantly correlated with a weakened CPM response and increased severity of pain and depression symptoms. The relationship between BMI and pain inhibition was distinctly non-linear, with detrimental effects becoming prominent beyond a BMI of 24 kg/m², marking a critical slope change point. Moreover, patients with a higher BMI did not benefit from pain inhibition on pain and depression scores, unlike their normal-weight counterparts, suggesting a disruption in the endogenous pain modulation mechanisms.

Conclusion

The study confirms that high BMI is detrimental to the clinical profile of FMS patients, adversely affecting pain inhibition and contributing to the severity of pain and depression, suggesting that weight management could be an integral component of FMS treatment.

Significance Statement

This study uniquely explores the relationship between BMI and pain inhibition response in fibromyalgia patients, revealing a non-linear association and highlighting BMI's role as a moderator of CPM. The findings emphasise that obesity disrupts endogenous pain regulation, leading to more severe pain and depression symptoms. This underscores the potential for weight management in FMS treatment and supports developing personalised interventions considering obesity status.