The above discussion of ways to differentiate bipolar from unipolar depression is also relevant to the general concept of a bipolar spectrum. The notion of a bipolar spectrum begins from the fact that many patients do not meet classical definitions of unipolar depression or bipolar disorder type I or II. As shown in Figure 1-1, many patients appear to demonstrate features of bipolarity such as the depressive phenomenology or the illness course mentioned above, and yet the inability to diagnose spontaneous manic or hypomanic episodes precludes the diagnosis of bipolar disorder types I or II.
It is important to realize that the bipolar spectrum concept, though relatively new (as resuscitated in recent years primarily by Akiskal; Ak-iskal 1996), is derived from Kraepelin's original manic-depressive illness concept (see Figure 1-2) (Kraepelin 1921). In Kraepelin's view, the key feature of manic-depressive illness—both the bipolar and recurrent unipolar forms—was recurrence. This contrasts with the current nosology (since DSM-III in 1980), which views polarity as the primary basis for diagnosing these mood disorders. In other words, the number of mood episodes the patient experienced, not what type of mood episode, was what mattered to Kraepelin. For DSM-III onward, what matters is the polarity of the episode (manic or depressive) and little else.
DSM-III, DSM-IV ICD-10
personality (RDC/ICD-9) disorder (DSM-III-R, DSM-IV)
FIGURE 1-2. The evolution of the bipolar/unipolar distinction from manic-depressive illness.
Note. BPI=bipolar disorder type I, BPII= bipolar disorder type II, D = major depression, d = subsyndromal depression, M = mania, m=hypomania, NOS=not otherwise specified, RDC=Research Diagnostic Criteria. Source. Reprinted from Goodwin FK, Ghaemi SN: "An introduction and history of affective disorders," in Oxford Textbook of Psychiatry, Vol 1. Gelder MG, Lo-pez-Ibor JJ Jr, Andreasen NC. Oxford, England, Oxford University Press, 2000, pp 677-680. Used with permission.
Various methods of classifying this bipolar spectrum have been proposed. One approach has been to provide further subtypes of bipolar illness (types III, IV, and so on) (Akiskal 2002). We have suggested another approach, which would be to combine all the further bipolar spectrum subtypes into a general category called "bipolar spectrum disorder"(BSD) (Ghaemi et al. 2002). A heuristic definition of BSD is provided in Table 1-4. Early research suggests that it may be a useful diagnosis that captures many patients with depressive disorders who are currently simply labeled as unipolar depressed patients. In one study of 87 consecutively referred young adults in an outpatient clinic, 83.9% were diagnosed with unipolar depression according to DSM-IV-TR. When bipolar spectrum disorder criteria were used, 47.1% of the total cohort were diagnosable with BSD (Smith et al. 2005). In one study of 61 patients with treatment refractory unipolar depression, 52% of the DSM-IV-TR unipolar group were diagnosable under this definition of BSD (Sharma et al. 2005).
TABLE 1-4. A proposed definition of bipolar spectrum disorder
A. At least one major depressive episode
B. No spontaneous hypomanic or manic episodes
C. Either of the following, plus at least two items from criterion D, or both of the following plus one item from criterion D:
1. A family history of bipolar disorder in a first degree relative
2. Antidepressant-induced mania or hypomania
D. If no items from criterion C are present, six of the following nine criteria are needed:
1. Hyperthymic personality (at baseline, nondepressed state)
2. Recurrent major depressive episodes (>3)
3. Brief major depressive episodes (on average, <3 months)
4. Atypical depressive symptoms (DSM-IV-TR criteria)
5. Psychotic major depressive episodes
6. Early age at onset of major depressive episode (< age 25)
7. Postpartum depression
8. Antidepressant wear-off (acute but not prophylactic response)
9. Lack of response to > 3 antidepressant treatment trials
Source. Reprinted from Ghaemi SN, Ko JY, Goodwin FK: "The Bipolar Spectrum and the Antidepressant View of the World." Journal of Psychiatric Practice 7:287-297, 2001. Used with permission.
Future clinical research will need to clarify whether it makes sense to keep a very broad and heterogeneous definition of unipolar depression in contrast with a very narrow and homogeneous definition of bipolar disorder. These studies suggest that some further broadening of the bipolar concept makes scientific and clinical sense.
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