Variable Voxel-based Morphometry Observations of Gray Matter Differences in Fibromyalgia: Individual Differences or Methodological Inconsistency?

Abstract

Fibromyalgia is a prevalent chronic pain condition characterized by widespread pain and sensory hypersensitivity. While much remains to be learned about the neurobiological underpinnings of this condition, alterations to the central nervous system appear to be heavily implicated in fibromyalgia's pathophysiology. Previous research examining brain structural abnormalities among fibromyalgia patients has yielded inconsistent findings. Thus, we followed previous voxel-based morphometry methods in magnetic resonance imaging to examine brain gray matter differences in females (n=17) with fibromyalgia and female healthy controls (n=17). We hypothesized that, relative to healthy control participants, fibromyalgia participants would exhibit lower gray matter volume in regions consistently implicated in pain processing and, specifically, fibromyalgia: the anterior cingulate cortex and the medial prefrontal cortex. Previously reported peak coordinates are located in both the anterior cingulate cortex (ACC) and medial prefrontal cortex (mPFC), but interpretation of these locations is varied. Therefore, we first examined a large region of interest that encompassed both the mPFC and ACC, followed by a whole brain analysis. Group differences were analyzed with two-sample t-tests, controlling for total intracranial volume. No significant differences in regional or whole brain gray matter volumes were detected between fibromyalgia patients and healthy controls. These results add to an existing body of disparate findings regarding brain gray matter volume differences in fibromyalgia, and suggest structural differences previously detected among fibromyalgia patients should be rigorously examined for reproducibility and support the need for additional meta-analyses. Absent significant differences may also suggest that individual differences, rather than methodological variability, account for contradictory results. Grant support from K99DA040154.