Research report
Threshold and subthreshold bipolar disorders in the Sesto Fiorentino Study

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Abstract

Background

The DSM IV lifetime prevalence for bipolar affective disorders is reported to be between 0.4% and 1% in most surveys. DSM IV, however, fails to identify the cases clinically significant described as bipolar spectrum. The few researches that have attempted to evaluate the prevalence of these disorders in the community report lifetime prevalence figures of 5% to 10% for the whole spectrum.

Method

The data from the Sesto Fiorentino Study, a community survey conducted by clinical interviewers using a typically clinical instrument, have been re-analysed. 2363 people out of the 2500 randomly selected in order to be representatives of the population aged 14 or more living in Sesto Fiorentino (44,000 inhabitants, Central Italy) could be evaluated according to a two-phase design.

Results

The lifetime prevalence rates were 0.47% for bipolar I disorder, 0.38% for bipolar II (0.85% for DSM IV bipolar disorders). A much greater number of subjects had clinically significant hypomanic symptoms that failed to fully satisfy the diagnostic criteria, totalling to 4.66% of the population. Compared with depressives without any sign of bipolarity (N = 297), these “subthreshold bipolar” cases had significantly greater comorbidity for Generalised Anxiety Disorder, Obsessive–Compulsive Disorders and Anorexia Nervosa, as well as with Obsessive–Compulsive Passive–Aggressive, Paranoid, Borderline personality disorders. Their depressive symptom pattern cases differed from that of the “pure” unipolar cases for a significantly greater frequency of psychic agitation, psychotic symptoms and hyperphagia.

Limitations and conclusions

The main limitation of the study is its retrospective nature, whereas it confirms the clinical relevance of even softer forms of bipolarity on epidemiological grounds.

Introduction

Although attenuated forms of “folie circulaire” were well described in the past (Falret, 1854), most of the community surveys of psychiatric disorders have considered only bipolar I disorder, consistently showing that it represents a relatively rare diagnosis with lifetime prevalence rates ranging from 0.4% to 1.8% (Weissman et al., 1996, Angst, 1998, Waraich et al., 2004, Jacobi et al., 2005). Bipolar II disorder has been included in fewer epidemiological studies and, contrary to expectations, it does not seem much more frequent than bipolar I disorder, with lifetime prevalence rates ranging between 0.5% and 2.0% in most surveys (Angst, 1998).

It has been suggested that these rates are likely to underestimate the real extension of the phenomenon, due to the excessively narrow criteria for hypomania required by the current diagnostic criteria (Angst, 1998, Angst et al., 2003a). Several authors have challenged the existing operational diagnostic criteria for hypomania on the basis of the observations conducted in clinical samples and suggested the existence of a much wider and highly prevalent bipolar spectrum (Akiskal and Mallya, 1987, Cassano et al., 1992, Akiskal, 1996, Akiskal and Pinto, 1999, Benazzi, 2003a). However, it may be objected that the high prevalence of subthreshold bipolar disorders in clinical samples could be due to a methodological artifact. In fact, since even soft signs of bipolarity imply a more severe course of illness, such cases might be overrepresented in clinical settings. These observations need therefore confirmation from epidemiological studies.

In the Zurich Cohort Study, broadening the diagnostic criteria for bipolar II disorder led to prevalence rates for the expanded bipolar spectrum of 5.5% or 10.9% employing respectively a “hard” (basically corresponding to the DSM IV criteria, except for the duration) or a “soft” definition of hypomania. The soft definition of hypomania was defined simply as ‘any hypomanic symptoms’, regardless of the duration and the consequences. Interestingly, both the “hard” and the “soft” bipolar II subgroups differed significantly from subjects with unipolar depressive disorders on diagnostic validators such as the family history for bipolar disorder, substance abuse, overactivity (Angst, 1998, Angst et al., 2003a, Angst et al., 2003b). The Zurich study has notable methodological strengths, including a long follow-up period (since 1979) with six successive interviews conducted by interviewers with clinical experience. However, skeptics may contend that the interview employed in the Zurich study puts an uncommon emphasis on the elicitation of even the milder hypomanic symptoms, thus possibly overinflating the prevalence rates. Angst's criteria for hypomania seem in fact exceedingly broad and likely to include a variety of forms that are not real expressions of bipolar illness. Having a couple of signs of euphoria–irritability–hyperactivity for one day does not necessarily mean having a mild bipolar disorder. On clinical grounds, having mild euphoria in a subject who has been suffering from depression may be truly considered as an indicator of soft bipolarity, whereas the same presentation in a subject with no evidence of depression does not automatically allow the same interpretation.

Regrettably, few other community studies have reported prevalence rates and correlates for bipolar spectrum disorders. A Hungarian community study (Szadoczky et al., 1998) and a re-analysis of the U.S. Epidemiologic Catchment Area database (Judd and Akiskal, 2003) and a recent Brazilian survey (Moreno and Andrade, 2005) found lifetime prevalence rates of 5.1%, 6.4% and 8.3% respectively.

These studies employed either the Diagnostic Interview Schedule (DIS) (Robins et al., 1981) or the Composite International Diagnostic Interview (CIDI) (World Health Organization, 1990). Both are fully structured interviews for use by lay interviewers with no clinical experience and the validity of such instruments in the evaluation of manic/hypomanic symptoms is highly questionable, since a poor correlation with the assessments made by experienced clinicians has been repeatedly reported (Goodwin and Jamison, 1990, Ghaemi et al., 2002, Benazzi, 2003b, Regeer et al., 2004, Jacobi et al., 2005).

A subsample of respondents of the NEMESIS (a Dutch national survey which employed the CIDI, ten Have et al., 2002) reinterviewed by clinicians using a semistructured interview, suggested an indirect estimate for a lifetime prevalence of 5.2% for bipolar spectrum disorders (Regeer et al., 2004).

Lewinsohn et al. (1995) employed a semistructured interview administered by clinicians in a sample of high school adolescents. They reported prevalence rates of approximately 1% for threshold and of 5.7% for subthreshold bipolar disorders. The methodology of this study is accurate but the sample cannot be considered as fully representative of the general population.

The purpose of the present study is to contribute to the knowledge of the epidemiology of the bipolar spectrum by presenting prevalence rates and correlates for threshold and subthreshold bipolar disorders from a general population study conducted by interviewers with clinical experience who used a semistructured interview.

Section snippets

Methods

Background and methods of the Sesto Fiorentino Study have been described in detail elsewhere (Faravelli et al., 2004a, Faravelli et al., 2004b). Briefly, the Sesto Fiorentino study was planned in order to study a community sample, using medical interviewers and typical clinical research instruments. The structure of the Italian National Health System (NHS) helped to these purposes. It is in fact free and covers the entire population. Actually, in the area where the study was conducted (the

Results

16 subjects met both criterion A and criterion B for manic episode. 5 of them, however, could not be diagnosed as bipolar disorder due to the exclusion criteria, i.e. not better accounted for by a psychotic disorder, thus leaving 11 subjects (lifetime prevalence 0.47%).

Nine cases met all the criteria for hypomania and could receive a diagnosis of bipolar II disorder.

89 cases satisfied criterion A, but failed to meet criterion B because of a number of symptoms lesser than three.

Five cases

Discussion

This study may be criticizable under several regards. It is well known that the retrospective evaluation of mild hypomanic symptoms is extremely difficult and often unreliable. We tried to combine the psychiatric assessment with the information deriving from the treating GPs, these being the figures who generally knew well their patients. It may be objected that the GPs may not be reliable in recognizing the minor symptoms of mood elation during the screening procedure. They were, however,

Conclusion

Our research is in line with previous reports suggesting high prevalence rates for bipolar spectrum disorders. Moreover, the differences between subthreshold bipolars and unipolar depressives further supports the validity of the concept of bipolar spectrum. As reported by Angst et al. (2003b), even the subjects with “soft” signs of subclinical hypomania have features that distinguish them from the true unipolars. This supports, on epidemiological grounds, the position contended by many

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