Obsessive-compulsive disorder (OCD) is a common, chronic, and disabling disorder marked by obsessions and/or compulsions that are egodystonic and cause significant distress to the patients and their families. During the last 25 years, there has been a resurgence of studies into various aspects of OCD, including epidemiological, pathophysiological, and pharmacological investigations. With the progress in finding effective treatments for OCD, different algorithms for the management of these patients have been developed. The progress in OCD includes advanced methodologies of imaging studies (both before and after treatment), along with insight into the neurological aspects of OCD and OCD-related conditions, leading to selective treatments.

Up to the early 1980s, OCD was considered a rather rare, treatment-refractory, and chronic condition of psychological origin. Dynamic psychotherapy was of little benefit and several pharmacological treatments were attempted without much success.⁽¹⁾ Since then, several researchers have reported that the prevalence of OCD is around 2 per cent in the general population.^(2,3) In addition, numerous studies have reported on the efficacy of various serotonin reuptake inhibitors, and consequently an understanding of the biological basis of OCD has begun to unfold.

The observation that clomipramine, a tricyclic antidepressant with a serotonergic profile, is effective in treating symptoms of OCD^(4,5) has increased interest in OCD in general and in the relationship between serotonin and OCD in particular. Substantial evidence currently suggests that OCD is almost unique among psychiatric disorders, as only serotonergic medications appear to be effective in this disorder.⁽⁶⁾ For example, non-serotonergic drugs, such as desipramine, a potent antidepressant and antipanic agent, are entirely ineffective in OCD.^{(7, 8 and 9)} This specific response to serotonergic drugs has paved the way for further research on the role of serotonin in the pathogenesis of OCD in particular, and in OCD-related disorders in general.

The lifetime prevalence of OCD in the general population is between 2 and 3 per cent (i.e. it is more prevalent than schizophrenia).^(2,10) This rate has been confirmed across different cultures.⁽³⁾ The prevalence of OCD among children and adolescents appears to be as high as among adults.⁽¹¹⁾ However, Nelson and Rice⁽¹²⁾ and Stein et al.⁽¹³⁾ have suggested that the diagnosis of OCD by the Diagnostic Interview Schedule administered by lay people leads to overdiagnosis, and so have proposed lower prevalence rates of 1 to 2 per cent.

Men and women are equally likely to be affected, although some reports have suggested a slight female predominance.⁽³⁾ During adolescence, boys are more commonly affected than girls. The mean age of onset is about 20 years of age. Single people are more commonly affected, probably representing the difficulty for people with OCD to maintain a relationship.

Patients with OCD are commonly afflicted by other mental disorders; for instance, the lifetime prevalence for a major depressive episode in these patients is around 67 per cent.^(3,14) Other common comorbid psychiatric diagnoses include alcohol-use disorders, social phobia, specific phobia, panic disorder, eating disorders, and post-traumatic stress disorder (PTSD).⁽¹⁵⁾ The comorbidity with schizophrenia and with tic disorders raises interesting pathophysiological and therapeutic implications. The rate of tic disorders approaches 40 per cent in juvenile OCD, and there is an increase in the prevalence of Tourette’s syndrome among the relatives of OCD patients.⁽¹⁶⁾

The relationship between OCD and obsessive-compulsive personality disorder (OCPD) has been a focus of debate. Although prospective research is lacking, it appears that OCPD is not a prominent risk factor for developing OCD, as the prevalence of OCPD among patients with OCD is not far from its prevalence in other psychiatric disorders.

The diagnosis of OCD according to DSM-IV criteria is based on the presence of either obsessions or compulsions, which cause marked distress, are time-consuming (more than an hour per day), or significantly interfere with the person’s normal routine and social and occupational activities. It stipulates that, at some point during the course of the disorder, but not necessarily during the current episode, the person has recognized that the obsessions or compulsions are excessive or unreasonable. However, if the patient does not recognize for most of the time during the current episode that the obsessions and compulsions are excessive or unreasonable, the diagnosis is OCD with poor insight.

If another Axis I disorder is present, it is mandatory that the content of the obsessions or compulsions is not restricted to it (e.g. a preoccupation with food or weight in eating disorders, or guilt feelings in the presence of a major depressive episode). The disturbance should not be due to the direct effects of a substance (e.g. of a drug abuse or a medication) or a general medical condition.

The obsessions are recurrent, intrusive, and distressing thoughts, images, or impulses, whereas the compulsions are repetitive, seemingly purposeful, behaviours that a person feels driven to perform. Obsessions are usually unpleasant and increase a person’s anxiety, whereas carrying out compulsions reduces anxiety. Resistance to carrying out a compulsion results in increased anxiety. The patient usually realizes that the obsessions are irrational and experiences both the obsession and the compulsion as egodystonic.

Patients with both obsessions and compulsions constitute at least 75 per cent of the affected patients, with most patients presenting with multiple obsessions and compulsions. The symptoms may shift, for example a patient who had washing rituals during childhood may present with checking rituals as an adult.

OCD can express itself in many different symptoms, but the classical presentations include washing, checking, aggressive, religious, or sexual obsessions, and ordering, counting, hoarding, and symmetry compulsions. Dimensional approaches have been used to analyze these characteristic subtypes, and present the different symptoms in an innovative way.⁽¹⁷⁾

The most common pattern is an obsession with dirt or germs, followed by washing or avoiding presumably contaminated objects (doorknobs, electrical switches, newspapers, people’s hands, telephones). Because it is hard to avoid the feared object is (e.g. faeces, urine, dust, or germs), patients wash their hands excessively and sometimes avoid leaving home because of their fear of germs. A second common pattern is an obsession of doubt, followed by a compulsion of checking. The person checks whether the oven is turned off or the front and back doors are closed—the checking may involve many trips back home to recheck what had already been checked. In OCD, the checking, instead of resolving uncertainty, often contributes to even greater doubt, which leads to further checking. The patients exhibit obsessional self-doubt, and feel guilty for having committed some damage (for instance, a fear of hurting someone while driving, leading to driving back over the same spot again and again). Other patterns include hoarding and religious obsessions. More recently, a dimensional approach to OCD has been launched by Leckman and colleagues, stating four symptom dimension of OCD: obsessions/checking, symmetry/ ordering, contamination/cleaning, and hoarding.^(17,18) Another pattern of OCD involves intrusive obsessional thoughts without a compulsion. Such obsessions are usually repetitious thoughts of some sexual or aggressive act that is reprehensible to the patient. Still another pattern is the need for symmetry or precision, which leads to a compulsion of slowness. Patients can take hours to eat a meal or shave, in an attempt to do things ‘just right’. Unlike other patients with OCD, these patients usually do not resist their symptoms.

The gap between the knowledge that the symptoms are irrational on one hand and the overwhelming urge to perform them on the other hand contributes to the immense suffering associated with OCD.

Many patients with OCD may have an onset of symptoms after a stressful event (e.g. pregnancy, a loss, or a sexual problem). Owing to the secretive nature of the disorder, there is often a delay of 5 to 10 years before patients come to psychiatric attention. However, the delay may shorten due to increased public awareness to the disorder through articles, books, and movies. The course of OCD is
usually long, but variable; some patients experience a fluctuating course, while others experience a chronic course.⁽²¹⁾

About 20 to 30 per cent of the patients show a significant improvement in their symptoms, and 40 to 50 per cent a moderate improvement. The remaining 20 to 40 per cent become chronic or their symptoms worsen.

OCD patients are prone to depression and sometimes even to suicide. A poor prognosis is indicated by yielding (rather than resisting) to compulsions, a early onset, male gender, tic related forms of OCD with associated to hoarding/symmetry compulsions, the need for hospitalization, psychotic features, a coexisting major depressive disorder, delusional beliefs, the presence of overvalued ideas (i.e. some acceptance of the obsessions and compulsions), and the presence of personality disorder (especially schizotypal personality disorder).^{(22, 23 and 24)} A good prognosis is indicated by good social and occupational adjustment and less avoidance.⁽²¹⁾ The obsessional content does not seem to be related to the prognosis, except for hoarding, which is usually considered to have a less favourable outcome.