Does work on obsessive-compulsive spectrum disorders contribute to understanding the heterogeneity of obsessive-compulsive disorder?

Background: There is a growing literature on the concept of an obsessive-compulsive spectrum of disorders. Here, we consider the different dimensions on which obsessive-compulsive spectrum (OCSDs) lie, and focus on how the concepts from this literature may help understand the heterogeneity of obsessive-compulsive disorder (OCD). Methods: A computerized literature search (MEDLINE: 1964-2005) was used to collect studies addressing different dimensions on which the OCSDs lie. Against this backdrop, we report on a cluster analysis of OCSDs within OCD. Results: OCSDs may lie on several different dimensions. Our cluster analysis found that in OCD there were 3 clusters of OCD spectrum symptoms: (1) "Reward deficiency" (including trichotillomania, pathological gambling, hypersexual disorder and Tourette's disorder), (2) "Impulsivity" (including compulsive shopping, kleptomania, eating disorders, self-injury and intermittent explosive disorder), and (3) "Somatic" (including body dysmorphic disorder and hypochondriasis). Conclusions: It is unlikely that OC symptoms and disorders fall on any single phenomenological dimension; instead, multiple different constructs may be required to map this nosological space. Although there is evidence for the validity of some of the relevant dimensions, additional work is required to delineate more fully the endophenotypes that underlie OC symptoms and disorders.