Although Kraepelin (1921) grouped most major forms of depression under the general rubric of "manic-depressive illness," it was not until Leonhard's (1957) work that patients with both depressive and manic episodes, whom Leonhard termed "bipolar," were distinguished from those exhibiting only recurrent depressions. Since 1957, more than 100 studies have examined the family history, natural course, clinical symptoms, personality factors, biology, and pharmacological treatments associated with the bipolar-unipolar distinction (e.g., Depue & Monroe, 1978; Goodwin &
Jamison, 1990; Johnson & Kizer, 2002). Within the bipolar category, a group of disorders appear to form a continuum or spectrum from the milder, subsyndromal form of manic depression, known as "Cyclothymia," to full-blown manic depression, known as Bipolar I Disorder. Indeed, the Diagnostic and Statistical Manual of Mental Disorders (4th ed., DSM-IV; American Psychiatric Association, 1994) identified four types of bipolar disorders: Bipolar I Disorder, Bipolar II Disorder, Cyclothymic Disorder, and Bipolar Disorder Not Otherwise Specified (NOS).
According to DSM-IV, Bipolar I Disorder is defined by at least one episode of mania. Symptoms of mania include euphoria and/or irritability, high energy/activity, rapid speech and increased talkativeness, racing thoughts, high self-confidence/grandiosity, decreased sleep, distracta-bility, and impulsive, reckless behaviors with a high propensity for negative consequences. Individuals with Bipolar I Disorder may have had prior depressive episodes and most will have subsequent manic or depressive episodes. They may also experience hypomanic episodes and mixed depressive/manic episodes. The lifetime prevalence of Bipolar I Disorder is approximately 1.2% (Smith & Weissman, 1992), with community samples yielding prevalence estimates ranging from 0.4% to 1.6% (Weissman, Bruce, Leaf, Florio, & Holzer, 1990). Completed suicide occurs in 10% to 15% of individuals with Bipolar I Disorder (DSM-IV; APA, 1994). Unlike unipolar depression, Bipolar I Disorder is equally common in men and women (Weissman et al., 1988) and has a mean age of onset of around 24 years, with many onsets in adolescence and even childhood (Geller & DelBello, 2003; Goodwin & Jamison, 1990). Bipolar I Disorder is associated with episodic antisocial behavior, divorce, and school or occupational failure (DSM-IV; APA, 1994; Hammen, Gitlin, & Altshuler, 2000). With regard to familial pattern, first-degree biological relatives of individuals with Bipolar I Disorder have elevated rates of Bipolar I (4%-24%), Bipolar II (1%-5%), and Major Depressive (4%-24%) Disorders (Goodwin & Jamison, 1990).
Bipolar II Disorder differs from Bipolar I in that individuals exhibit one or more hypomanic, instead of full-blown manic, episodes accompanied by the presence of one or more major depressive episodes. Bipolar II Disorder is more common in women than in men and its lifetime prevalence is estimated at approximately 0.5% (Weissman et al., 1988). As in Bipolar I Disorder, completed suicide occurs in from 10% to 15% of cases, and the associated psychosocial impairment is also similar. DSM-IV (APA, 1994) reports a familial pattern for Bipolar II, with first-degree biological relatives exhibiting elevated rates of Bipolar II, Bipolar I, and Major Depressive Disorders.
Cyclothymic Disorder is characterized by recurrent and intermittent mood episodes in which the individual oscillates, or "cycles," between pe riods of depression and hypomania, with or without normal, euthymic periods in between. However, unlike major depression and mania, both types of mood episodes are of subsyndromal intensity and duration (2-3 days, on average; Alloy & Abramson, 2000). Historically, there has been controversy about whether Cyclothymia is best conceptualized as a temperament, a personality disorder, or a subsyndromal mood disorder (Alloy & Abramson, 2000). Friends and family often describe cyclothymic individuals as "moody," "high-strung," "hyperactive," and "explosive" (Akiskal, Djenderedjian, Rosenthal, & Khani, 1977), and they are often perceived as exhibiting features of personality disorder rather than mood disorder at first clinical presentation.
However, Kraepelin (1921) believed that Cyclothymia is on a continuum with full-blown Bipolar I Disorder and, indeed, may be a precursor to it. Five lines of evidence support this continuum model and suggest that Cyclothymia is an integral part of the bipolar spectrum (Alloy & Abramson, 2000). First, the behavior of cyclothymics is qualitatively similar to that of individuals with Bipolar I and II Disorders (Akiskal et al., 1977; Akiskal, Khani, & Scott-Strauss, 1979; Depue et al., 1981). Second, similar to Bipolar I and II patients, cyclothymics show high rates of comorbidity of anxiety, alcohol and substance use, eating, and attention deficit hyperactivity disorders (Alloy, Flannery-Schroeder, Safford, Floyd, & Abramson, 1999; Brady & Lydiard, 1992; Pergui, Toni, & Akiskal, 1999). Third, equivalent rates of bipolar disorder have been found in the first-and second-degree relatives of cyclothymic and Bipolar I individuals (Akiskal et al., 1977; Depue et al., 1981; Dunner, Russek, Russek, & Fieve, 1982), and increased rates of Cyclothymia are found in the offspring of Bipolar I patients (Klein, Depue, & Slater, 1985). In addition, among mono-zygotic twins, when one twin was diagnosed with manic depression, the co-twin, if not also manic depressive, was frequently cyclothymic (Bertelsen, Harvald, & Hauge, 1977). These findings suggest that Cyclothymia shares a common genetic predisposition with bipolar disorder. Fourth, like Bipolar I patients, cyclothymics often experience an induction of hypomanic episodes when treated with tricyclic antidepressants (Akiskal et al., 1977) and often improve on lithium prophylaxis (Akiskal et al., 1979). Finally, up to 80% of bipolar patients exhibit cyclothymia premor-bidly (Goodwin & Jamison, 1990); cyclothymics are at increased risk of developing full-blown bipolar disorder in the future (Akiskal et al., 1977).
In DSM-IV, Bipolar Disorder NOS includes individuals with bipolar features that do not meet criteria for Bipolar I, Bipolar II, or Cyclothymic Disorders. Such cases include recurrent hypomanic episodes without intercurrent depressive symptoms or rapid alternation between manic/ hypomanic symptoms and depressive symptoms that do not meet minimal duration criteria for a manic, hypomanic, or depressive episode.
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