Increased gray matter density in young women with chronic vulvar pain

Provoked vestibulodynia (PVD) is a common form of chronic vulvar pain with unknown aetiology. Central pain regulatory mechanisms have been suggested to be disrupted in PVD, and consequently, PVD may be associated with anatomical changes in pain modulatory brain areas. Here, we compared total gray matter volumes and regional gray matter densities between 14 medication-free young women with relatively short-standing PVD (1 to 9 yrs) and 14 control subjects using whole brain voxel-based morphometry (VBM). VBM revealed that PVD subjects had significantly higher gray matter densities in pain modulatory and stress-related areas, i.e. the parahippocampal gyrus/hippocampus and basal ganglia (globus pallidus, caudate nucleus, and substantia nigra). In several of these regions, gray matter was related to clinical symptoms, namely lowered pain thresholds and increased pain catastrophizing scores. No region showed decreased gray matter density in the PVD group. These results point at the morphological alterations in supra-spinal pain modulatory circuitry, which might contribute to the clinical symptoms of patients with PVD. Previous VBM studies in older subjects with a longstanding chronic pain condition have demonstrated gray matter decreases in similar areas. We therefore speculate that gray matter density might increase in young pain patients with short disease duration and decrease in older subjects with longstanding disease, similarly to some psychiatric conditions, in which bi-directional changes of gray matter have been observed.