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Obsessive–compulsive disorder (OCD) has enjoyed a resurgence of scientific interest since the Epidemiological Catchment Area (ECA) study in the USA suggested that it is not at all a rare disorder; indeed, it became known as the ‘hidden epidemic’, testament to the alleged degree of hitherto unrecognised morbidity in the general population. But how common is OCD really? As with any of the anxiety disorders, the symptoms associated with OCD are extremes on a normal continuum, and the stage at which they become a ‘disorder’ is a moot point. The DSM rubric of ‘significant distress’ or ‘impairment of functioning’ is useful enough, but fails to reflect the fact that subjective appraisal of these parameters is often incompatible with objective considerations. For example, an agoraphobia sufferer who is entirely confined to her house by her fears, might not consider herself to be significantly distressed (because the feared situations are always avoided), nor impaired in functioning (because her family has rallied around, support and cosset her, doing the shopping for her, etc.). However, any objective measure of functioning would undoubtedly rate her as impaired. The obverse of this is that some individuals rate themselves as very distressed and disabled by anxiety symptoms, while more objective appraisal does not bear this out.
A question of definition
In a study to assess the validity of the ECA data, Anthony and colleagues investigated the extent to which DIS diagnoses of OCD (and other disorders) tallied with expert clinician diagnosis. Concentrating on the Baltimore ECA site, a subsample of the DIS interviewed cohort were independently assessed by psychiatrists, and all available data were then subjected to a ‘clinical reappraisal’ (CR) by psychiatrists. For DSM-III defined OCD, the 1-month prevalence rate according to the DIS was 1.3%, while the CR figure was 0.3%. What is more worrying is that the proportion of DIS-positive OCD cases that were also considered cases by CR, was 0.04. In terms of statistical agreement between the two diagnoses, the kappa was only 0.05. In a separate study, Nelson and Rice re-interviewed individuals ascertained as ‘cases’ of OCD in the ECA study, after an interval of 1 year and reported a stability of diagnosis of only 0.2 (kappa statistic). Put another way, only 56 (19%) of the 291 original OCD ‘cases’ were re-diagnosed at 1 year. Individuals with obsessions and compulsions were twice as likely to have a ‘stable’ diagnosis, as were those with an early onset of illness. A further example of the problems associated with making a definitive diagnosis of OCD in a large-scale epidemiological study, is the investigation by Stein et al. from Canada. In this study, lay interviewers used a telephone version of the Composite International Diagnostic Interview (CIDI), to interview a general population sample of 2261 people. Fully 26.2% of the sample reported having experienced obsessions, and 22.2% compulsions. However, few of these individuals considered their obsessions and compulsions to be unreasonable or excessive, repetitive or recurrent, or excessively time-consuming (> 1 h/day); thus, only 69 people (3.1%) met DSM-IV criteria for OCD. However, when a subsample of these ‘cases’ was re-interviewed by research personnel, using the Structured Clinical Interview for DSM-IV (SCID), only one-quarter were considered truly to meet DSM-IV criteria, giving a revised 1-month prevalence of 0.6%. The majority of discordance between the CIDI-positive and SCID-positive cases was due to a labelling of ordinary sources of worry or concern as ‘obsessions’, and a tendency to accept reports of ‘distress’ and ‘disability’ too readily, on the basis of patient report. One way around some of these problems is to ascertain symptoms, rather than define ‘caseness’ as such. Some indication of the utility of this approach can be found in those epidemiological studies which have adopted the Present State Examination (PSE), which essentially determines presence or absence of symptoms, either currently, or over the individual’s lifetime. In the study of Bebbington et al., the PSE was used to interview a stratified subsample of 310 of an original 800 people randomly selected from the general population of Camberwell, southeast London. The PSE questions pertaining to OCD included items on checking, washing and ruminations; rates were 9.1%, 1.6%, and 0.9%, respectively.
Looked at another way, however, the actual number of ‘cases’ of OCD, on clinical review by a psychiatrist, was only one patient with OCD ‘severe enough to warrant treatment’; many other individuals with OCD symptoms were considered to have manifested these symptoms secondary to another disorder (mostly depression), or to have symptoms too mild to warrant treatment. So, how common is OCD? The question is unanswerable, the answer dependent upon the definition of the disorder, and the internal ‘boundaries’ imposed by diagnostic systems. A range of anything from 0.05% to 3.50% lifetime prevalence is possible to defend, a close to one hundred-fold difference. Perhaps more useful is focusing our attention, as clinicians, on individuals, and their particular symptoms, and how these symptoms are perceived by them and how they impact on their lives. If we are unclear about the ‘internal’ boundaries of OCD (i.e. what precise set of symptoms are required to be present for the diagnosis), we are equally unclear about the ‘external’ boundaries of the disorder.
Thus, there are a number of other psychiatric and neuropsychiatric disorders whose symptomatology shows many similarities with OCD. This raises important questions with respect to whether some of these disorders might have aetiological links, and/or share similar pathogenetic mechanisms, with OCD. To inform these issues, we turn now to a consideration of the external boundaries of OCD, with a review of the so-called ‘OCD spectrum’.
Obsessive–compulsive spectrum disorders
The other psychiatric disorders which have been considered to fall within the OCD spectrum can also be considered to lie on an impulsive–compulsive continuum of ‘risk avoidance’. As Hollander puts it, impulsive individuals are seen as ‘risk seekers who try to maximise pleasure, arousal or gratification’, while compulsive individuals ‘attempt to avoid harm or reduce anxiety or discomfort, associated with the rituals’. In this model, disorders such as sexual compulsions and impulsive personality disorders would be considered ‘impulsive’, and hypochondriasis, body dysmorphic disorder, and anorexia nervosa, ‘compulsive’. This model has more than heuristic attraction. Indeed, there is some evidence of different neurochemical substrates of disorders at either end of the continuum. For example, impulsive disorders show a response to serotonergic agents characterised by a rapid response which attenuates over time, while disorders at the compulsive end of the spectrum tend to have a lag time before onset of response, but tend to maintain their gains.
An overlap with psychosis?
Having said this, it has long been recognised that a patient with an evolving psychotic process can present with obsessive–compulsive symptoms; the unwary clinician can be misled and delay appropriate antipsychotic therapy. In more established cases of schizophrenia, OCD is also overrepresented. For example, Eisen et al. found that 6 (7.8%) of 77 patients with schizophrenia or schizoaffective disorder also met DSM-III-R criteria for OCD. In an early consideration of this overlap, Stengel explored the ‘interrelationship between neurotic manifestations and psychotic reaction types’, and concluded that ‘the excessive inclination of the obsessional neurotics to reality proving and doubt affected their attitude to psychotic experiences in a favourable way’. Thus, he foreshadowed the current vogue for cognitive–behavioural interventions for individuals with psychotic symptomatology.
An overlap with Axis II disorders?
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