Epidemiological studies of personality disorders carried out in psychiatric settings

Ta.b.le.3 lists the median prevalence rates for any PDs found in 32 studies carried out in inpatient and outpatient psychiatric samples and published between 1981 and

1998. Only those prospective studies that surveyed homogeneous clinical samples (either inpatients or outpatients) of more than 100 subjects have been considered for this analysis. The second column shows the number of studies on which the median prevalence rate is based.

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Table 3 Median prevalence rates of PDs among psychiatric patients in prospective studies including more than 100 subjects

In these studies subjects have been directly evaluated for the purpose of obtaining PD rates, by means of a standardized assessment instrument specific for PDs. Several other studies, which have evaluated only the prevalence of specified PDs in clinical samples, are not shown here.

In general, the prevalence of PDs among psychiatric outpatients and inpatients is quite high, with a majority of studies ( n = 17) showing a PD prevalence rate higher than 50 per cent of the sample. However, it is difficult to draw more definite conclusions from these studies, because of substantial differences in sampling, diagnostic criteria, assessment methods, availability of mental health services, prevalence of Axis disorders, and sociocultural factors.

There are, however, some consistencies across studies that deserve consideration. The most prevalent PD seems to be borderline, both in inpatient and in outpatient settings. The next most common PDs are schizotypal and histrionic. These three disorders are also characterized by the lowest social functioning. They are especially common in inpatient settings, as their symptomatology often results in the patient being admitted to hospital due to their suicidal behaviour, substance abuse, and cognitive-perceptual abnormalities. In outpatient settings, dependent and passive-aggressive PD are also common.

Especially in inpatient settings, many people who meet the criteria for one PD also meet the criteria for other PDs. (4 ,46) The highest comorbidity rate appears to occur with borderline PD, with the frequent coexistence of borderline and histrionic PDs, followed by antisocial, schizotypal, and dependent PDs.

With regard to comorbidity between PDs and Axis I disorders, the most common and best-studied patterns are between substance abuse and PDs, affective disorders and PDs, and anxiety disorders and PDs (particularly borderline, antisocial, avoidant, and dependent PDs). Other clinically significant associations have been found between bulimia nervosa and borderline PD, as well as between anorexia and avoidant PD.(47) High rates of PD (especially borderline and antisocial PDs) have also been detected in patients with selected medical conditions, such as HIV-positive patients. (48)

Some studies have assessed the treated prevalence of PD using administrative data (e.g. discharge figures, psychiatric case register data, etc.). In the United States, using data from the 1993 National Hospital Discharge Survey, Olfson and Mechanic(49) found that almost 12 per cent of patients discharged from public general hospitals had a diagnosis of PD, compared with 11 per cent of patients from non-profit hospitals and 5 per cent of patients from proprietary general hospitals. In England and Wales, 7.6 per cent of all admissions and 8.5 per cent of first admissions over a 1-year period were diagnosed as having PDs. (5.°.)

Some investigations, which compared the hospital admission rates for PD over time, allow us to assess the impact of diagnostic changes. In Denmark, sex- and age-standardized rates of first-admitted borderline patients significantly increased during the 16-year interval between 1970 and 1985, and this might be explained in terms of a change in diagnostic habits.(51) In the United States, comparing the diagnoses given to inpatients in a large university-affiliated mental hospital in the last 5 years of the DSM-II era (n = 5143) with those given in the first 5 years of the DSM-III era (n = 5771), a marked increase (from 19 per cent to 49 per cent) was found in the diagnosis of PD, together with a decrease in the diagnosis of schizophrenia and a corresponding increase in the diagnosis of affective disorders. (52)

The epidemiological findings in treated samples are especially important if we bear in mind that the presence of a PD among those suffering from other mental disorders can be a major predictor of the natural history and treatment outcome. Therefore an important clinical implication of these findings is that patients in treatment because of severe Axis I disorders must be carefully assessed with an assessment instrument specific for PDs, because of the high likelihood of diagnosing a PD and the subsequent need to adjust their treatment accordingly.

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