A comparison of brain volume and cortical thickness in excoriation (skin picking) disorder and trichotillomania (hair pulling disorder) in women.

Skin picking disorder (SPD) and trichotillomania (hair pulling disorder, or HPD) significantly overlap in terms of clinical features. However, few studies have directly compared structural brain data in these disorders. The aim of this study was to compare volumes of brain structures and cortical thickness in patients with SPD and HPD, and determine involvement of fronto-striatal pathways. Seventeen female SPD, 17 HPD and 15 healthy age-matched controls underwent clinical assessment and structural MRI imaging. Group differences were determined in brain volume and cortical thickness, controlling for illness severity. Participants with SPD had greater volume of the ventral striatum bilaterally; and reduced cortical thickness in right hemisphere frontal areas, and greater thickness of the cuneus bilaterally compared to HPD and control participants. HPD participants demonstrated reduced thickness of the right parahippocampal gyrus compared to SPD and control participants. The findings here are partially consistent with previous structural work in SPD, and suggest some differences in the neurobiology of SPD and HPD. The more extensive involvement of the ventral striatum in SPD may suggest greater involvement of the reward system, while the more extensive involvement of the parahippocampal gyrus in HPD may be consistent with the dissociative symptoms often seen in these patients.