Alterations in cortical gray matter volume, thickness and surface area in women with fibromyalgia syndrome.

Aim of Investigation: Recent neuroimaging studies using voxel-based morphometry (VBM) demonstrated reductions in brain gray matter (GM) volume in Fibromyalgia (FS), a chronic pain syndrome thought to result from altered central pain processing. Little is known about the relative contribution of the two components of cortical GM volume – thickness and surface area – to these structural alterations. Our aim was to assess alterations in GM morphology (volume, thickness, area) in FS compared to a control group, and to correlate GM morphology with clinical variables of pain, namely duration, intensity (VAS), and tender point count, and with depression score (Center for Epidemiology Studies-Depression Scale). Methods: Twenty-three women with FS and 26 healthy pain-free women matched for age and educational level participated in the study. Pressure pain thresholds were measured with an algometer applied to the 18 defining tender points and to 10 additional points to obtain a total positive tender point count. A high-resolution structural T1-weighted brain scan (360 sagittal slices without gap; isotropic voxel size 0.5mm; FOV 240 x 240 x 180mm; TR 35ms; flip angle 50°; TE 5.7ms) was acquired for each subject, using a 3T Philips Achieva MR scanner. GM volume was assessed applying VBM to modulated data in SPM8 using an individualised DARTEL template for inter-subject alignment. Surface-based measures of cortical thickness and area were obtained using the Freesurfer 4.5.0 software. Both the VBM and Freesurfer data were spatially smoothed using an 8mm FWHM Gaussian kernel. The statistical analysis of the surface-based data was performed both on vertex-wise values and on values averaged within 64 anatomical Regions of Interest (ROIs). Nuisance influences of age, total intracranial volume (TIV), handedness and menopause were removed. Results: Compared to the control group, FS patients showed i) reduced GM volume in the left medial and superior frontal gyrus (BA 6; a trend that became significant after controlling for depression score), ii) reduced surface area in the left pericalcarine cortex, and iii) increased thickness in the left fusiform gyrus and in the right rostral middle frontal cortex. Pain intensity was negatively correlated with thickness in the bilateral paracentral lobule (BA 6); however, brain morphology was correlated neither with pain duration nor with positive tender point count. The only significant age-by-group interaction consisted in the fact that the age-related loss in GM thickness and area in the left lateral occipital cortex was less steep in patients compared to controls, because the patients had lower values already at a younger age. Conclusions: The present results provide further evidence for altered brain morphology in FS, including brain areas in which this had not been previously demonstrated, and show a relationship of specific structural changes with the severity of specific symptoms.