Special article
The bipolar spectrum: a clinical reality in search of diagnostic criteria and an assessment methodology

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Abstract

Failure to recognize subthreshold expressions of mania contributes to the frequent under-diagnosis of bipolar disorder. There are several reasons for the lower rate of recognition of subthreshold manic symptoms, when compared to the analogous pure depressive ones. These include the lack of subjective suffering, enhanced productivity, ego-syntonicity, and diurnal and seasonal rhythmicity associated with many of the manic and hypomanic symptoms, and the psychiatrists' tendency to subsume persistent or even alternating symptoms among personality disorders. Furthermore, the central diagnostic importance placed on alterations in mood distracts clinicians from paying attention to other more subtle but clinically meaningful symptoms, such as changes in energy, neurovegetative symptoms and distorted cognitions. Although officially accepted in both ICD-10 and DSM-IV, we believe bipolar II disorder is underdiagnosed because of inattention to symptoms of hypomania. Moreover, by requiring the presence of both full-blown hypomanic and major depressive episodes, current nosology fails to include symptoms or signs which are mild and do not meet threshold criteria. There is already agreement in the field that such symptoms are important for depression. We now propose that attention should also be devoted to mild symptomatic manifestations of a manic diathesis, even if such manifestations may sometimes enhance quality of life. The term `spectrum' is used to refer to the broad range of such manifestations of a disorder from core symptoms to temperamental traits. Spectrum manifestations may be present during, between, or even in the absence of, an episode of full-blown disorder. We have developed a structured clinical interview to assess the mood spectrum (SCI-MOODS) to evaluate the whole range of depressive and manic symptoms. This instrument is currently undergoing psychometric testing procedures. Similar to the SCID interview, the SCI-MOODS interview provides a separate rating for each of the major DSM-IV™ symptoms, but the latter also identifies and rates subthreshold and atypical manifestations. This paper presents the concept of a subthreshold bipolar disorder and discusses the potential epidemiological, diagnostic and therapeutic relevance of such a spectrum conditions. We also describe the SCI-MOODS interview used reliably to identify the occurrence of a bipolar spectrum condition. Obviously a great deal of systematic research needs to be conducted to ascertain the reliability and validity of subthreshold bipolarity as summarized in this paper and embodied in our instrument.

Introduction

Both classical (Kraepelin, 1921) and contemporary (Akiskal, 1983, Goodwin and Jamison, 1990) observations support the thesis that bipolarity is expressed along a severity spectrum. The progress of clinical therapeutics over the past two decades has expanded the boundary of bipolar disorder and its varied phenomenology and epidemiology. Within the same period there has been considerable interest in identifying subclinical and/or subthreshold expressions of this disorder (Akiskal, 1983, Akiskal and Mallya, 1987, Akiskal, 1996). However, these subtle forms of bipolar disorder still are overlooked both in clinical settings and epidemiological studies. Subthreshold mania has been described using a myriad of clinical labels including soft, subtle, partial, incomplete, mild, atypical, subliminal and attenuated. We believe that none of the descriptions provided to date provides a complete definition encompassing the full range of characteristics of subthreshold mania. We also believe the terms themselves are somewhat inaccurate and potentially misleading. For example, the term `soft' (Akiskal and Mallya, 1987), could suggest inadvertently a lack of solid, clear form of symptomatology, or the term `subtle' might refer to a fine and elusive symptomatology that can be difficult to recognize.

In this paper, we use the term `subthreshold bipolar spectrum' for those patients who show features of bipolar disorder, but whose symptoms are not severe enough to fulfil the diagnostic criteria of ICD-10 (WHO, 1992) and DSM-IV (APA, 1994) for bipolar disorder. The entire bipolar spectrum encompasses conditions with typical DSM-IV bipolar symptoms that are clinically significant and almost meet the criteria of a bipolar disorder subtype (Bipolar NOS according to the DSM-IV), as well as those that meet symptom criteria but are considered `subclinical' in that they do not cause impairment to the individual and/or do not require treatment. However, bipolar spectrum may also be diagnosed if there are atypical symptoms or personality traits not found in the criteria section of DSM-IV or ICD-10, but indicative of a bipolar diathesis.

We believe that the accuracy of diagnosis of bipolar disorder could be improved through the introduction of a refined procedure for the detection and evaluation of a broader range of symptoms relevant to mania. For example, identification of different forms of manic symptoms including psychotic or confused/stuporous symptoms and subthreshold symptoms could be helpful in making a diagnosis (Akiskal, 1983Akiskal, 1996Angst, 1995).

This paper argues that systematic study of the spectrum of bipolar symptoms using a structured clinical interview will be relevant to the diagnosis, treatment and epidemiology of bipolar disorder. Indeed, as Angst (1995)has recently argued, subthreshold syndromes frequently demand treatment and one should not underestimate the severity of their social impact and treatment needs.

Section snippets

The need to better delineate the manic/hypomanic component of bipolar disorder

The DSM-IV™ criteria for a manic episode are fairly limited, perhaps in part because of the stigma associated with a diagnosis of manic-depressive illness. Recently, there has been interest in subthreshold depression and anxiety (Judd et al., 1994, Olfson et al., 1996, Akiskal et al., 1997), but relatively less attention has been given to subthreshold mania. Under-diagnosis of subthreshold forms of mania may lengthen the time to recognition of illness and this could delay treatment and worsen

Bipolar II disorder

Although hypomanic manifestations received extensive coverage in Kraepelin's treatise on manic-depressive insanity (Kraepelin, 1921), bipolar II as a specified bipolar subtype was first described by Dunner et al. (1976)at NIMH.

BP II disorder, as currently defined in the DSM-lV™, shows diagnostic stability (Angst, 1986, Coryell et al., 1987, Coryell, 1996), a greater risk of the same disorder among the relatives of an affected subject (Coryell et al., 1984, Endicott et al., 1985), a high

Bipolar III disorder

Subthreshold bipolar manifestations were characterized in a sample of 687 patients selected for the presence of an index episode of major depression in a collaborative study with the Universities of Pisa and Tennessee (Musetti et al., 1989, Cassano et al., 1992b). Patients whose UP depression arose from a `hyperthymic' temperament (UP-HT), were compared with groups of patients with BP I, BP II and `pure' UP. We found UP-HT subjects were similar to the bipolar patients on some characteristics,

Mixed presentations of subthreshold bipolar spectrum

Kraepelin (1921)first described mixed states as the coexistence of depressive and manic symptoms. Since his classic description, mixed states have not received extensive research evaluation. The clinical manifestations of mixed states are polymorphic (Dell'Osso et al., 1991) and include psychotic forms, with incongruous delusions and hallucinations (Akiskal and Puzantian, 1979, Dell'Osso et al., 1993, Perugi et al., 1997) as well as milder and sub-clinical conditions (Akiskal and Mallya, 1987),

SCI-MOODS: A structured clinical interview for the mood spectrum

Although our spectrum concept in no way rejects the DSM™ or ICD™ affective categories, it does provide a broader range of symptoms allowing for the possibility that there is not a clear distinction between different DSM mood categories. We see our conceptualization similar to Kraepelin (1921)when he created the rubric of `manic-depressive insanity' that for him spanned from the mildest affective to the most extreme psychotic. By including altered mood and mood related features in one spectrum

Concluding remarks

Patients affected by brief-recurrent or chronic subthreshold bipolar syndromes should not be considered as “a group of subjects where symptoms failed to meet the threshold for a diagnosis” (Angst, 1997). The current diagnostic manuals (DSM-IV™ and ICD-10™) tend to exclude all but `threshold psychiatry', thus reflecting the trends in some countries to limit psychiatry (both clinical intervention and research) to established diagnostic groups. The current state of these manuals also reflects the

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