The bipolar spectrum

The two-dimensional bipolar spectrum described here comprisesa continuum of severity from normal to psychotic and a continuumfrom depression, via three bipolar subgroups to mania. Thiscombination of dimensional and categorical principles for classifyingmood disorders may help alleviate the problems of underdiagnosisand undertreatment of bipolar disorders.

INTRODUCTION

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INTRODUCTION

Depression is very distressful, prompts the depressed personto seek treatment and is relatively easy to diagnose. Hypomania,on the other hand, is often perceived as normal well-beingand tends not to be reported. There is wide agreement as tothe difficulty of identifying hypomania in bipolar II and minorbipolar disorders: patients with bipolar depression report thatthe recognition of their disorder was delayed by as much as8–10 years. Unipolar depression, which is defined bythe absence of hypomania or mania, remains an uncertain diagnosislifelong. Over decades of recurrent depressive illness, bipolardisorder may manifest at any time: a lifelong follow-up of patientshospitalised showed a persistent risk of diagnostic change tobipolar disorder of 1.25% per year of observation.

Bipolar affective disorder is a more severe disorder than majordepression, as measured by higher lifelong recurrence and greatercomorbidity with psychiatric disorders, especially anxietyand secondary substance use disorders. In addition it is associatedwith serious somatic disorders such as diabetes, hypertensionand cardiovascular disease. This explains the correspondinglyhigher mortality rates among people with bipolar disorder, althoughthe suicide risk is lower in type I bipolar disorder than in depression (Ösby et al, 2001).

Correct diagnosis of bipolar illness is essential for appropriate treatment, especially long-term secondary prophylaxis. As aconsequence of their severity, unrecognised bipolar disorderslead, moreover, to higher costs than major depression, butthese can be considerably reduced by early diagnosis and treatment,as recently shown by McCombs et al (2006).

The underdiagnosis of mood disorders, especially bipolar disorders,is not confined to the clinical setting but may also applyto traditional epidemiological studies, which found lifetimeprevalence rates of 0.5–2%. Some recent studies (Kessler et al, 2003;Lieb, 2006) comprising two or three interview waves have described growing lifetime prevalence rates for both major depressiveepisodes (19% to 24%) and for bipolar disorder types I andII together (about 2% to 4%). An important question, then,is what proportion of patients with major depression shouldin fact be diagnosed as having bipolar disorder: is it one-fifthor one-tenth as generally reported, or as many as half, aswe have found?

BIPOLAR SPECTRUM: A MODEL FOR RESEARCH AND CLINICAL PRACTICE

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BIPOLAR SPECTRUM: A MODEL...

The development of a validated bipolar spectrum concept canprovide a more differentiated research and treatment modelfor affective disorders and may help reduce the underrecognitionof bipolarity.

A dimensional concept (from normal to pathological) was proposedby Kretschmer in 1921 for schizophrenia (schizothymic –schizoid – schizophrenic) and for affective disorders(cyclothymic temperament – cycloid `psychopathy' –manic-depressive disorder) as well as by Bleuler (1922). Theterm `spectrum' was first used in psychiatry in 1968 for theschizophrenia spectrum, which integrated schizoid personalities(Kety et al, 1968). In 1977 Akiskal proposed a cyclothymic–bipolarspectrum and in 1981 Klerman suggested a mania spectrum (Akiskal, 1977; Klerman, 1981).

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Fig. 1 Two-dimensional mood/affective spectrum (does not include schizoaffective disorder, as a transition to the schizophrenic spectrum). The precise relationship of personality disorders to the disease spectra is uncertain and an unsolved general problem of psychiatric classification. BP-I (-II), bipolar-I disorder type I (II); D, major depression, d, minor depression; M, mania; m, hypomania; MDD, major depressive disorder; RBD, recurrent brief depression; sx, symptoms

Today the term `bipolar spectrum' is mainly used in two complementary senses (Fig. 1):

a spectrum of severity, which embraces psychotic and non-psychoticmajor and minor bipolar disorders (including bipolar dysthymia,recurrent brief and minor depressions), cyclothymic disorders,hypomania and, at its broadest, even borderline disorders andcyclothymic temperament;
a proportional mood spectrum, whichconsiders the two componentsmania and depression, first onthe level of major mood disorders– major depression(D) bipolar II disorder (Dm), bipolarI disorder (MD), maniawith mild depression (Md) and pure mania(M) (Angst, 1978)– and then on the level of minor mooddisorders: thecorresponding categories are mild depression(d), minor bipolardisorder (md) and hypomania (m).

This proportional model is an extension of Kleist's conceptof bipolar disorder as a combination of the two monopolar disordersdepression and mania (Kleist, 1937, 1953). This model hasproved fruitful not only in incorporating bipolar I and bipolarII disorders but also in differentiating mania with or withoutmild depression (Md/M) from bipolar I disorder (MD). Maniais not identical to bipolar I disorder in terms of family history,course and suicide risk, and on the sub-threshold level hypomaniais not the same as minor bipolar disorder or cyclothymic disorderin terms of family history and temperament.

Both the above bipolar spectrum concepts are dimensional innature, having no natural categorical subgroups. Epidemiologicaland clinical studies have demonstrated the continuous distributionof depressive and hypomanic/manic symptoms and syndromes fromnormal to pathological. Psychiatric symptoms in consultingpopulations have been shown to be dimensional (Goldberg, 2000).Moreover, in a 20-year follow-up, patients with type I andtype II bipolar disorder were found to spend about half thetime in sub-threshold affective conditions, and these weredimensional, involving the full range of symptom severity of depression and hypomania (Judd et al, 2003). Most healthypeople report depressive and hypomanic symptoms and many areidentifiable as manifesting depressive, hypomanic and cyclothymictemperaments, which appear to predispose to the respectiveaffective disorders and personality disorders (see Fig. 1).Only about 15% of the population report no such symptom overtheir lifetime and are `super-normal', with very low scoresfor vegetative lability and neuroticism.

CASENESS

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CASENESS

The dimensional nature of the mood spectrum raises the questionof the correct cut-off levels for caseness (Wing et al, 1978).The current concept of bipolar-II disorder requires a diagnosisof hypomania in addition to major depression. However, thedefinition of hypomania is the subject of much controversy andresearch. It is generally agreed that the DSM–IV criteria (American Psychiatric Association, 1994) are too strict (notsensitive) and not based on empirical evidence (not validated).All aspects of the definition are under discussion: the qualityof the stem questions (criterion A), which are restricted to elevated and irritable mood (i.e. do not consider symptomsand signs of increased activity), the number and nature ofsymptoms required and the minimum duration of an episode. Aduration of under 4 days (2 days or 1 day) and the presenceof two or three instead of three or four of the seven symptomsof hypomania are now proposed and have been partially validated.As with depression, brief spells of hypomania (1–3 days)are far more common than manifestations lasting 4 days or 1week. In order to improve the recognition of bipolarity, wehave proposed a sub-diagnostic concept consisting of a fewhypomanic symptoms of brief duration associated with a lifetimediagnosis of depression.

What we need today is an empirically validated, sensitive definitionof hypomania, which will allow early recognition of major andminor bipolar disorders. Promising modern screening instrumentsfor the self-assessment of hypomanic symptoms have now beendeveloped such as the Mood Disorder Questionnaire (Hirschfeld et al, 2000)and the Hypomania Checklist–32 (Angst et al, 2005), butthere is still no gold standard for valid cut-off points forcaseness on these continuous measures: that would depend ona validated definition of hypomania, which is still lacking.A similar problem is present in measures of temperament, whereclear distinctions between depressive, hyperthymic and cycloid(`cyclothymic') personality disorders are desirable.

THE FUTURE

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THE FUTURE

It may take longer than hoped to develop better-validated diagnostic criteria: apart from genetic data, long-term follow-up studiesover at least 10 years are needed in order to approach diagnosticclassifications that can be used as gold standards. For thisreason the forthcoming ICD–11 and DSM–V may againhave to give us definitions with a limited half-life.

Too many studies, especially in epidemiology, have used methodstailored and restricted to the current DSM–IV diagnosticconcepts and have not collected additional data which wouldhave allowed those concepts to be questioned – and toomany journals and reviewers hesitate to accept papers thatdeviate methodologically from the current diagnostic conservatism. At the other extreme, the promising bipolar spectrum conceptcan be discredited by uncritical generalisations and over-inclusiveness,for instance by taking for granted that cyclothymic personalityor borderline disorders are validated elements of the bipolarspectrum. These hypotheses may be correct, but we need muchmore genetic and follow-up evidence to support them.

We can safely assume that the prevalence of bipolar disordersis seriously under-reported and that the burden of bipolardisorder, estimated by the World Health Organization to bemuch lower than that of depression, will as a consequence haveto be reassessed.

The mood spectrum is also embedded in the spectrum of functionalpsychoses, including schizophrenia and schizoaffective andaffective disorders. There is growing clinical evidence thatthe spectrum approach, with its dimensional nature, offersa real alternative to the traditional Kraepelinian dichotomyof schizophrenia v. manic-depressive insanity (Marneros, 2006)and the unipolar–bipolar dichotomy. Moreover, in agreementwith clinical genetic studies (Angst & Scharfetter, 1990),modern molecular genetic studies demonstrate that there is noclear-cut distinction between schizophrenia and bipolar affectivedisorder; both clinically and genetically they share many features (Craddock & Owen, 2005).

Diagnostic concepts of psychiatric syndromes are purely descriptiveand cannot constitute diseases (Kendell, 1999). The proposedmood spectrum model unifies categorical classification, whichis essential, with a dimensional view, which is true to nature;both are needed and both are empirically testable.

REFERENCES

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