Individuals with body dysmorphic disorder (BDD) suffer from preoccupations with perceived defects in physical appearance, causing severe distress and disability. Although BDD affects 1–2% of the population, the neurobiology is not understood. Discrepant results in previous volumetric studies may be due to small sample sizes, and no study has investigated cortical thickness in BDD. The current study is the largest neuroimaging analysis of BDD. Participants included 49 medication-free, right-handed individuals with DSM-IV BDD and 44 healthy controls matched by age, sex, and education. Using high-resolution T1-weighted magnetic resonance imaging, we computed vertex-wise gray matter (GM) thickness on the cortical surface and GM volume using voxel-based morphometry. We also computed volumes in cortical and subcortical regions of interest. In addition to group comparisons, we investigated associations with symptom severity, insight, and anxiety within the BDD group. In BDD, greater anxiety was significantly associated with thinner GM in the left superior temporal cortex and greater GM volume in the right caudate nucleus. There were no significant differences in cortical thickness, GM volume, or volumes in regions of interest between BDD and control subjects. Subtle associations with clinical symptoms may characterize brain morphometric patterns in BDD, rather than large group differences in brain structure.
Body dysmorphic disorder (BDD) is an under-studied psychiatric disorder, despite its relatively high prevalence (1–2%) (Mufaddel et al., 2013). Individuals with BDD are preoccupied with perceived defects in their physical appearance (American Psychiatric Association, 2013). These concerns are often obsessive, resulting in significant distress and disability. Due to similar symptoms, heredity, and comorbidity, BDD is conceptualized as an obsessive-compulsive related disorder (Phillips et al., 2010). BDD is also associated with depression and anxiety. In addition, those with BDD often have low insight into their psychiatric illness and exaggerate perceived “defects,” even though they are not noticeable or very slight to others (American Psychiatric Association, 2013).
There have only been a small number of neuropsychological and neuroimaging studies in BDD, and its neurobiology remains largely unknown. Of the four studies of brain morphometry in BDD (Rauch et al., 2003, Feusner et al., 2009, Atmaca et al., 2010 and Buchanan et al., 2014), two found greater total white matter (WM) volume (Rauch et al., 2003 and Atmaca et al., 2010) and two found smaller volumes in frontostriatal systems (anterior cingulate and the orbitofrontal cortices) (Atmaca et al., 2010 and Buchanan et al., 2014). However, these studies had small sample sizes, and the results are discrepant. Moreover, these studies investigated whole brain or region of interest (ROI) volume measurements, but they did not assess gray matter (GM) thickness, which may be a more sensitive tool to uncover subtle or diffuse morphometric abnormalities.
Neuropsychological, psychophysical, and functional magnetic resonance imaging (fMRI) studies suggest that the pathophysiology of BDD involves abnormalities in executive functioning, visuospatial processing and memory, processing of emotional faces, and visual systems (for review, see Madsen et al., 2013). Several fMRI studies demonstrate an imbalance of global versus detailed processing when BDD patients view images of their own and others׳ faces and of objects (Deckersbach et al., 2000, Feusner et al., 2007, Feusner et al., 2010, Feusner et al., 2011 and Jefferies et al., 2012). Two studies found abnormal hypoactivity in primary and/or secondary visual processing systems, and one also found hyperactive frontostriatal systems for own-face stimuli. Abnormal neural activity plays a role in BDD, but whether there are structural abnormalities in these systems has not been established.
This is the first study to examine cortical thickness in individuals with BDD, and the largest to investigate brain morphometry. Differences in brain structure and function, specifically in visual processing regions of the brain, may underlie the dysfunctional preoccupation with details in physical appearance that are core BDD symptoms. We hypothesized that there would be regional differences (greater or lesser) in GM thickness and volumes between BDD patients and controls. Specifically, we expected between-group differences in frontostriatal and visual processing systems, where previous studies found abnormal volumes (Rauch et al., 2003, Atmaca et al., 2010 and Buchanan et al., 2014) and/or functioning (Feusner et al., 2007, Feusner et al., 2010 and Feusner et al., 2011). We also predicted significant associations between clinical symptoms and both cortical thickness and volumes. Knowledge of neuroanatomical abnormalities in BDD could contribute to mechanistic understandings of the pathophysiology.
