White matter microstructural integrity assessment in fibromyalgia using cardiac-gated diffusion tensor imaging

Fibromyalgia (FM) pathophysiology remains largely unknown, with considerable neuroimaging evidence that brain functional and structural characteristics of patients differ from those of controls. Studies using diffusion tensor imaging (DTI) to assess white matter (WM) microstructure have shown significant differences across several brain regions for FM patients when compared to healthy controls (HC), which may indicate WM abnormalities. The main aim of this study was to assess global and regional brain WM characteristics in FM patients and HC using DTI. Eighteen female FM patients and 18 age- and gender-matched HC underwent a single magnetic resonance imaging (MRI) session where cardiac-gated DTI data with isotropic voxels (2 mm3) were acquired in a 3T scanner. To assess group differences in WM microstructure, we estimated DTI metrics such as fractional anisotropy (FA), mean diffusivity (MD) and radial diffusivity (RD) in a voxelwise fashion, and we performed a region of interest (ROI) analysis restricted only to the WM regions serving nociceptive pathways in the brain. Compared to FM, HC showed a trend towards greater FA values over the right anterior corona radiata (cluster size=116 voxels), while FM patients demonstrated an increased MD (cluster=11,511) and RD (cluster=7,938) in several WM areas (p<0.1). ROI analyses showed that, compared to FM, HC had greater FA values (p=0.061) and greater axial diffusivity (p=0.077) in the right primary somatosensory cortex. FM patients had greater MD (p=0.036) and RD (p=0.079) over the left corticospinal tract. Although these are preliminary results from ongoing research and further investigation is needed, our analyses of DTI metrics suggest that FM patients show WM abnormalities that may be associated to enhanced pain processing in supraspinal centers.