White Matter Abnormalities in Skin Picking Disorder: A Diffusion Tensor Imaging Study

Skin picking disorder (SPD) is characterized by the repetitive and compulsive picking of skin, resulting in tissue damage. Neurocognitive findings in SPD implicate difficulty with response inhibition (suppression of pre-potent motor responses). This function is dependent on the integrity of the right frontal gyrus and the anterior cingulate cortices, and white-matter tracts connecting such neural nodes. It was hypothesized that SPD would be associated with reduced fractional anisotropy in regions implicated in top-down response suppression, particularly white-matter tracts in proximity of the bilateral anterior cingulate and right frontal (especially orbitofrontal and inferior frontal) cortices. 13-subjects meeting proposed SPD criteria for DSM-5 free from other current psychiatric comorbidities, and 12 healthy comparison subjects underwent MRI with a 3-T system. Between-group comparisons of imaging data underwent voxelwise analysis with permutation modeling and cluster correction. Fractional anisotropy (measured using diffusion tensor imaging) was the primary outcome measure. Subjects with SPD exhibited significantly reduced fractional anisotropy in tracts distributed bilaterally, which included the anterior cingulate cortices. Fractional anisotropy did not correlate significantly with SPD disease severity, or depressive or anxiety scores. These findings implicate disorganization of white-matter tracts involved in motor generation and suppression in the pathophysiology of SPD, findings remarkably similar to those previously reported in trichotillomania. This study adds considerable support to the notion that—in addition to the phenomenological and comorbid overlap between SPD and trichotillomania—these disorders likely share overlapping neurobiology.