White matter microstructure in body dysmorphic disorder and its clinical correlates

Abstract

Body dysmorphic disorder (BDD) is characterized by an often-delusional preoccupation with misperceived defects of appearance, causing significant distress and disability. Although previous studies have found functional abnormalities in visual processing, frontostriatal, and limbic systems, no study to date has investigated the microstructure of white matter connecting these systems in BDD. Participants comprised 14 medication-free individuals with BDD and 16 healthy controls who were scanned using diffusion-weighted magnetic resonance imaging (MRI). We utilized probabilistic tractography to reconstruct tracts of interest, and tract-based spatial statistics to investigate whole brain white matter. To estimate white matter microstructure, we used fractional anisotropy (FA), mean diffusivity (MD), and linear and planar anisotropy (c(l) and c(p)). We correlated diffusion measures with clinical measures of symptom severity and poor insight/delusionality. Poor insight negatively correlated with FA and c(l) and positively correlated with MD in the inferior longitudinal fasciculus (ILF) and the forceps major (FM). FA and c(l) were lower in the ILF and the inferior fronto-occipital fasciculus and higher in the FM in the BDD group, but differences were nonsignificant. This is the first diffusion-weighted MR investigation of white matter in BDD. Results suggest a relationship between impairments in insight, a clinically important phenotype, and fiber disorganization in tracts connecting visual with emotion/memory processing systems.

Fig. 1. Correlations between white matter diffusion measures and poor insight/delusionality in bilateral white matter tracts in BDD group (N=14)

Correlation between scores on the BABS (a measure of degree of poor insight/delusionality) and FA, MD, c_l and c_p in bilateral ILF, IFOF, and FM BABS = Brown Assessment of Beliefs Scale; FA = fractional anisotropy; MD = mean diffusivity; GI = geometric indices; c_l = linear anisotropy; c_p = planar anisotropy; ILF = inferior longitudinal fasciculus; IFOF = inferior longitudinal fasciculus; FM = forceps major * Indicates significant P values after Bonferroni correction for multiple comparisons