This supplement to CNS Spectrums focuses on the obsessive-compulsive spectrum of disorders and their relationship to anxiety. Hollander and others pioneered the concept of the obsessive-compulsive spectrum in the early 1990s, and have described its breadth and overlap with other psychiatric disorders. While its place in the psychiatric nomenclature is uncertain, the obsessive-compulsive spectrum is intertwined with the anxiety disorders in both its symptoms and biologic substrates.

Obsessive-compulsive disorder (OCD) has an important place at the center of the spectrum. While currently classified in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition as an anxiety disorder, OCD is distinct from these conditions in the International Classification of Diseases. There is a strong rationale for its separation from the anxiety disorders. First, OCD often begins in childhood, whereas other anxiety disorders typically have a later age of onset. OCD has a nearly equal gender distribution, unlike the other anxiety disorders, which are more common in women. Studies of psychiatric comorbidity show that, unlike the other anxiety disorders, persons with OCD generally tend not to have elevated rates of substance misuse. Family studies suggest that first-degree relatives of persons with OCD have an elevated prevalence of OCD-related disorders including body dysmorphic disorder, hypochondriasis, and grooming disorders, but not other anxiety disorders except for generalized anxiety disorder. The brain circuitry that mediates OCD appears to be different from that involved in other anxiety disorders. Lastly, OCD is unique with regard to its specific response to selective serotonin reuptake inhibitors, while noradrenergic medications, effective in the anxiety and mood disorders, are largely ineffective. On the other hand, the benzodiazepines, which have little effect on OCD, are often effective for the other anxiety disorders.