Psychology, neurocognition, and neurobiology in body dysmorphic disorder: similarities and differences with obsessive-compulsive disorder

The aims of this thesis were to advance current knowledge of body dysmorphic disorder (BDD), and contribute to an improved understanding of overlaps and differences between BDD and obsessive-compulsive disorder (OCD). Four research studies were undertaken in pursuit of these aims. In the first study, a systematic literature review of existing research which had directly compared BDD and OCD groups was performed, to delineate similarities and differences between the disorders. The results demonstrated similarities between BDD and OCD in broad clinical features, elevated perfectionism, and fear of negative evaluation; yet BDD differed from OCD in demonstrating poorer illness insight, visual processing alterations, impaired facial affect recognition, and increased social anxiety. However, the review highlighted a paucity of research in psychological phenomenology, general neurocognition, and neurobiology in BDD as compared to OCD. Further exploration of these areas through narrative literature reviews led to the development of three subsequent research studies.
Studies 2, 3 and 4 each involved direct comparison of individuals with BDD (with no history of OCD), individuals with OCD (with no history of BDD), and healthy controls. Study 2 investigated self-referential psychological constructs of identity functioning, self-ambivalence, internalised shame and self-esteem among these groups. While both BDD and OCD participants demonstrated significantly greater identity difficulties and self-ambivalence as compared to controls, BDD participants also displayed greater internalised shame and poorer self-esteem than both OCD and controls. These data suggest that internalised shame and poor self-esteem might be important distinguishing features of BDD from OCD. Study 3 compared neurocognitive functioning among the three groups using a comprehensive cognitive battery, and additionally explored for the possibility of neurocognitive heterogeneity within BDD and OCD using cluster analysis. While initial comparisons found no significant between-group differences for neurocognitive performance, cluster analysis identified three distinct subgroups within BDD and OCD. These subgroups were characterised by intact neurocognition (41%), under-performance within normative range (30.8%), or impaired performance on multiple cognitive domains (28.2%). An equal presence of BDD and OCD participants within each subgroup further suggested that the disorders share highly similar neurocognitive profiles, both at a group-average level, and in neurocognitive subgroups. Finally, Study 4 examined the resting-state functional connectivity of intrinsic brain networks, using independent components analysis of functional-magnetic resonance imaging data. BDD and OCD were found to show similar connectivity alterations in two networks typically involved in higher-order neurocognition (central executive and right fronto-parietal networks). However, BDD significantly differed from OCD in the connectivity of a sensorimotor and an auditory network. Further differences between BDD and control participants were identified in the default mode, posterior visual, sensorimotor, and cerebellar networks, the pattern of which indicated a profile of altered somatic and internally-focused bodily processing in BDD relative to controls. Overall, the results of this thesis add novel information to current understanding of BDD, and to knowledge of overlaps and differences between BDD and OCD. These findings have implications for future research and current theoretical models of BDD in psychological, neurocognitive and neurobiological domains. Moreover, the thesis findings carry implications for nosological conceptualisations of BDD, as well as suggestions for improved clinical understanding and treatment of the disorder.