Research report
Toward a re-definition of subthreshold bipolarity: epidemiology and proposed criteria for bipolar-II, minor bipolar disorders and hypomania

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Abstract

Background: The boundaries of bipolarity have been expanding over the past decade. Using a well characterized epidemiologic cohort, in this paper our objectives were: (1) to test the diagnostic criteria of DSM-IV hypomania, (2) to develop and validate criteria for the definition of softer expressions of bipolar-II (BP-II) disorder and hypomania, (3) to demonstrate the prevalence, clinical validity and comorbidity of the entire soft bipolar spectrum. Methods: Data on the continuum from normal to pathological mood and overactivity, collected from a 20-year prospective community cohort study of young adults, were used. Clinical validity was analysed by family history, course and clinical characteristics, including the association with depression and substance abuse. Results: (1) Just as euphoria and irritability, symptoms of overactivity should be included in the stem criterion of hypomania; episode length should probably not be a criterion for defining hypomania as long as three of seven signs and symptoms are present, and a change in functioning should remain obligatory for a rigorous diagnosis. (2) Below that threshold, ‘hypomanic symptoms only’ associated with major or mild depression are important indicators of bipolarity. (3) A broad definition of bipolar-II disorder gives a cumulative prevalence rate of 10.9%, compared to 11.4% for broadly defined major depression. A special group of minor bipolar disorder (prevalence 9.4%) was identified, of whom 2.0% were cyclothymic; pure hypomania occurred in 3.3%. The total prevalence of the soft bipolar spectrum was 23.7%, comparable to that (24.6%) for the entire depressive spectrum (including dysthymia, minor and recurrent brief depression). Limitation: A national cohort with a larger number of subjects is needed to verify the numerical composition of the softest bipolar subgroups proposed herein. Conclusion: The diagnostic criteria of hypomania need revision. On the basis of its demonstrated clinical validity, a broader concept of soft bipolarity is proposed, of which nearly 11% constitutes the spectrum of bipolar disorders proper, and another 13% probably represent the softest expression of bipolarity intermediate between bipolar disorder and normality.

Introduction

Although the psychopathology of hypomania was described in great detail in the nineteenth century by Jules Falret, 1878, Falret, 1879, and the term hypomania coined very soon thereafter by Mendel (1881), it took almost a century to define hypomania operationally, and that definition is still in a state of flux today. Minimum duration, stem criteria, and the number of signs and symptoms are three areas of requiring a good deal more systematic investigation. The minimum duration required for a diagnosis has changed significantly over the years; it was 2 days in the Research Diagnostic Criteria (Spitzer et al., 1978), not specified in DSM-III or DSM-III-R, and 4 days in DSM-IV, and recently a group of bipolar experts recommended to revert back—on the basis of extensive evidence—to the minimum of 2 days (Akiskal et al., 2000). Elevated, expansive or irritable mood, the stem criterion A of DSM-IV mania, has also been questioned, with Akiskal et al. (2001) recently suggesting that activation be considered as a stem criterion, a finding in line with his original recommendation (Akiskal et al., 1977) that observed behavioural excesses to be given precedence to mood swings in the diagnosis of cyclothymic disorder. This has also been the approach taken in the Zurich study in Switzerland (Angst, 1992). Finally the threshold of three or four out of seven signs and symptoms required for a diagnosis has yet to be validated.

It is very difficult to assess hypomania in the general population and in depressed patients who are unaware of their mood changes (Akiskal, 2002). Unlike most depressives, hypomanic subjects seldom complain of or suffer from their shifts in energy, activity and sleep behaviour but tend to experience them as positive. It is well known that such changes are more likely first to be picked up and recognised by family and friends. Thus, to focus in community studies—in the absence of collateral information from significant others — on mood changes as a gate to further probing may result in a very large number of false negative diagnoses.

It was these considerations that led us earlier to recommend (Angst, 1992) using a number of signs and symptoms of overactivity to probe for hypomania, and making relevant social consequences observed by others as obligatory criteria for the proper diagnosis of hypomania. On the basis of further analyses, we suggested removing episode-length as a diagnostic criterion. The proper definition of hypomania has important implications: it is decisive for diagnosing bipolar II disorder and subsyndromal bipolar disorder, which was found by Lewinsohn et al. (1995) to have considerable clinical validity and a prevalence rate of 5% in adolescents.

This paper will: (1) test several aspects of the diagnostic criteria of DSM-IV hypomania; (2) compare new, ‘hard’ and ‘soft’ definitions of bipolar-II (BP-II) disorder, minor bipolar disorder (MinBP) and hypomania; and (3) demonstrate the clinical validity and comorbidity of these disorders on the basis of new data from our prospective community cohort study.

Section snippets

The definition of hypomania in DSM-IV

The DSM-IV criteria for hypomania require: (A) a distinct period of at least 4 days of elevated, expansive or irritable mood; (B) the presence of three or more of seven diagnostic symptoms (four symptoms if the mood is only irritable); (C) an unequivocal change in functioning; (D) this change and disturbance is observable by others; (E) the episode does not meet criteria for mania; (F) the symptoms are not due to the effects of a substance or a general medical condition.

The Zurich study

Validity of some diagnostic criteria of DSM-IV hypomania

We analysed the following as validators for the diagnostic criteria of hypomania: positive family history rates for mania/hypomania and depression; age of onset for hypomanic or depressive symptoms; total number of days spent in hypomania, depression and in both over the previous 12 months; diagnosis of depression; treatment of depression; suicide attempts; lifetime comorbidity with anxiety disorders, substance and alcohol abuse/dependence; conduct problems in childhood/adolescence, and

Discussion

This paper consists essentially of two stages; in the first we test the validity of certain key DSM-IV diagnostic criteria for hypomania, and in the second we develop a new, broader concept based on hard and soft definitions of hypomania and bipolar disorders.

Subjects reporting overactivity but no mood changes did not significantly differ from those with mood changes (euphoria/irritability) in respect of the clinical validators. This finding strongly suggests that overactive behaviour should be

Limitations

The obvious limitations of this study are that (1) it deals with a cohort which does not represent all age groups; and (2) several of the analysed subgroups are relatively small. Replication of the results by studies based on larger community, preferably national, samples and investigating varying thresholds for defining a hypomanic syndrome would be necessary to replicate, modify or extend the present finding of very high prevalence of bipolar spectrum conditions. Of the total of 24%

Conclusion

We found in line with the clinical studies and conceptualization of Akiskal, 1983, Akiskal, 2002, Perugi et al. (1998), Benazzi and Akiskal (2003), and Lewinsohn et al. (2002, in press), strong evidence for the existence of a wide and highly prevalent spectrum of bipolar syndromes and hypomania in the general population, which is clinically relevant, and in many cases only treated for depression, and which is not identifiable by the current criteria of diagnostic manuals. This paper is a

Acknowledgements

This work was supported by Grant 3200-050881.97/1 of the Swiss National Science Foundation.

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