Progress in Neuro-Psychopharmacology and Biological Psychiatry
Review articleIs obsessive–compulsive disorder an anxiety disorder?
Introduction
Obsessive–compulsive disorder (OCD) is currently classified as an anxiety disorder in the Diagnostic and Statistical Manual of Mental Disorders (DSM) (American Psychiatric Association, 2000). Indeed, throughout most of the twentieth century, OCD has been viewed as an anxiety disorder or neurosis (Tynes et al., 1990). However, the notion of a spectrum of obsessive–compulsive (OC) related disorders that is comprised of such disparate disorders as OCD, body dysmorphic disorder, certain eating disorders, pathological gambling, and autism, is gaining acceptance. The fact that these disorders share obsessive–compulsive features and evidence similarities in patient characteristics, course, comorbidity, neurobiology, and treatment response raises the question of whether OCD is best conceptualized as an anxiety disorder or as part of an OC spectrum of disorders. In this article, we evaluate evidence from comorbidity and family studies, as well as biological evidence related to neurocircuitry, neurotransmitter function, and pharmacologic treatment response that bear on this issue. Because other articles in this issue cover the OC spectrum in detail, we will focus primarily on similarities and differences between OCD and other anxiety disorders and will be less concerned with research related to the OC spectrum (the reader is also referred to Hollander et al., 2005a, for an in-depth discussion of the OC spectrum). We conclude with a discussion of the implications of removing OCD from the anxiety disorders category and moving it to an OC spectrum disorders category, as is being proposed for the DSM-V.
Section snippets
The current nosology of obsessive–compulsive disorder
OCD is a debilitating disorder marked by two distinct phenomena: recurrent, disturbing, intrusive thoughts (obsessions) and overt repetitive behaviors or mental acts (compulsions) that are performed to reduce distress caused by obsessions. The most common obsessions concern thoughts about contamination, pathological doubt, and order/symmetry (Eisen and Rasmussen, 2002). Other obsessions include sexual obsessions as well as concerns about aggressive or horrific impulses (e.g., hurting a loved
The obsessive–compulsive spectrum disorders
In the past two decades the notion of an OC spectrum of related disorders has gained popularity (Hollander, 1993, Hollander et al., 2005a, Jenike, 1990, McElroy et al., 1994, Stein, 2002). The OC spectrum was proposed in response to observations that a number of disparate disorders, for example, body dysmorphic disorder, hypochondriasis, some eating disorders, and some impulse control disorders, share obsessive–compulsive features—that is, they are marked by obsessive thinking and/or compulsive
Is OCD an anxiety disorder? Comorbidity studies
One way to demonstrate a relationship between two disorders is to show that patients with disorder A are more likely to have disorder B and, conversely, that patients with disorder B are more likely to have disorder A; however, when evaluating comorbidity patterns it is important to consider whether the comorbid disorder is a long-term complication of the primary disorder.
Is OCD an anxiety disorder? Family studies
In addition to showing evidence of high comorbidity rates, a unique relationship between OCD and one or more other disorders would be supported by evidence showing increased prevalence of the disorder(s) in relatives of patients with OCD.
The neurocircuitry of OCD
Drawing upon functional neuroimaging data and earlier theorizing, Saxena and Rauch (2000) put forward a model for the pathophysiology of OCD that points to dysfunction in orbitofrontal–subcortical circuitry. This circuitry is thought to be comprised of a direct and an indirect pathway, both of which originate in the frontal cortex and project to the striatum. From the striatum, however, the direct pathway projects to the globus pallidus interna/substantia nigra, pars reticulate (GPi/SHr)
Is OCD an anxiety disorder? Neurotransmitter function and pharmacologic treatment response
A number of neurotransmitter systems have been implicated in anxiety disorders, in particular monoaminergic transmitters (i.e., norepinephrine, serotonin, and dopamine), amino acid transmitters (i.e., gamma aminobutyric acid (GABA) and glutamate), and peptidergic neurotransmitters (i.e., corticotrophin releasing hormone (CRH), neuropeptide Y, and substance P) (Charney, 2003). Evidence for the role of specific neurotransmitters is supported by neurochemical, pharmacologic, and neuroimaging
Commentary
In an effort to clarify the relationship between OCD and other anxiety disorders, including PTSD, panic disorder, specific and social phobia, and GAD, this article reviewed comorbidity and family studies as well as studies investigating neurocircuitry, neurotransmitter function, and treatment response. Studies investigating comorbidity patterns between OCD and other anxiety disorders are mixed: some suggest increased prevalence rates for current and lifetime anxiety disorders in OCD, whereas
Implications of changing OCD classification in the DSM-V
It is currently being proposed that OCD be removed from the anxiety disorders category in the DSM-V and clustered with other putative OC spectrum disorders. Removing OCD from the anxiety disorders category will likely highlight the distinct features of OCD and, hopefully, raise awareness about OCD, increasing the likelihood of detection and appropriate treatment. It is believed that many OCD cases go undetected because patients are embarrassed about their symptoms and, consequently, are
Acknowledgements
Preparation of this chapter was supported by grants from the National Institute of Mental Health, National Institute on Neurological Disorders and Stroke, National Institute on Drug Abuse, Food and Drug Administration and investigator initiated research grants from Solvay, Wyeth, Pfizer, and Ortho-McNeil.
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