Nosological Placement of Obsessive-Compulsive and Related Disorders: A Comprehensive Structural Analaysis

Large-scale investigations of structural models of psychopathology have identified several overarching factors that account for comorbidity among psychiatric syndromes: Internalizing, Externalizing, and Oddity/Psychoticism. Obsessive-compulsive disorder (OCD) is often excluded from these investigations. When it has been included, its placement in structural models of psychopathology is ambiguous; in some cases it has been a marker of Internalizing, the Internalizing subfactor Fear, and Oddity/Psychoticism. In DSM-5, OCD is newly classified in the Obsessive-Compulsive and Related Disorders (OCRDs) chapter, along with body dysmorphic disorder, hoarding disorder, hair pulling disorder, and skin picking disorder. Because these disorders have not been included in previous structural models, OCD's relative relation to the OCRDs, psychoticism/oddity symptoms, and anxiety disorder symptoms is unknown. The goals of the present analysis were to (a) examine the integrity of the OCRD category in structural models of psychopathology, (b) assess OCD's fit as an Internalizing, Oddity, and OCRD disorder, and (c) examine psychopathology structure at the symptom dimension level to examine the effects of specific symptoms on OCD's relations to other syndromes. Structural analysis identified five overarching factors: Distress, Fear, Externalizing, Oddity/OCRD, and Eating Disorder. The results provided partial support for an OCRD category, however were suggestive of an overlap between OCRD and Oddity syndromes. Furthermore, several OCRDs did not fit optimally within the OCRD factor; rather, BDD loaded with Distress and Illness Anxiety with Fear. Comparison of OCD's fit among these factors suggested that OCD's relation to other psychopathology is complex and multifaceted: OCD loaded with both Oddity/OCRD and Fear. Symptom-level analyses shed light on these results, indicating that OCD cleaning symptoms are related to specific phobias, whereas checking/ordering, obsessing, and neutralizing were more strongly related to Oddity/OCRD diagnoses. These results have important clinical and theoretical implications. First, this analysis informs future revisions of the DSM and suggests that the overlap between Oddity and OCRD should be reflected. Second, assessment of symptom dimensions will aid clinicians and researchers in understanding differential underlying mechanisms of mental illness. Finally, results call into question the theoretical underpinnings of the OCRD category and suggest the need to identify broader underlying mechanisms for observed comorbidity.