Diagnostic Features, Prevalence, and Impact of Bipolar Disorder

Terence A. Ketter, MD

Bipolar Disorders Clinic, Department of Psychiatry and Behavioral Science, Stanford University School of Medicine, Stanford, California

Diagnostic Features of Bipolar Disorder

Bipolar disorder shares symptoms of depression with unipolar depressive disorder, but is defined by episodes of mania or hypomania. Depression can include affective symptoms such as a pervasive sadness (depressed mood), a lack of pleasure or interest in activities (anhedonia/apathy), and irritability (in pediatric patients); cognitive symptoms such as decreased self-esteem and concentration, indecisiveness, feelings of guilt, and suicidal thoughts; and physical symptoms such as psychomotor retardation or agitation and either an increase or decrease in sleep, appetite, or energy. To be clinically noteworthy and a focus for treatment, major depressive episodes must involve 5 or more symptoms nearly every day for at least 2 weeks, at least 1 of which is pervasive sadness or anhedonia, and must cause substantive subjective distress or impairment. Major depressive episodes should be differentiated from sadness due to bereavement or from symptoms due to a medical disorder or substance use.1

In some ways the mirror image of depression, mania can include affective symptoms such as euphoric, expansive, or irritable mood; cognitive symptoms such as inflated self-esteem, distractibility, and racing thoughts; and behavioral symptoms such as increased psychomotor activity, increased goal-directed activity, and impulsivity.1 A distinctive (but not always present) symptom of mania is a decreased need for sleep. To be classified as a manic episode, a euphoric, expansive, or irritable mood must be present along with 3 or 4 additional symptoms and must last for at least 1 week or require hospitalization. (If the mood is merely irritable, 4 other symptoms are needed.) The DSM-IV-TR1 definition of mania requires that the mood disturbance be severe, entailing psychosis, hospitalization, or marked social or occupational impairment. Manic episodes that are the physiologic consequence of a medical disorder or substance use do not count toward a diagnosis of bipolar I disorder.

Hypomania is not as severe as mania and is thus mild to moderate.1 Indeed, some hypomanic episodes can involve enhanced function rather than deterioration of function. Hypomanic episodes must last at least 4 days; must be accompanied by at least 3 additional manic symptoms (or 4 if the mood is irritable rather than euphoric or expansive); must not involve psychosis, hospitalization, or marked social or occupational impact; and must not be due to a medical disorder or substance use.

Prevalence of Bipolar Disorder

Bipolar disorder in its broadest sense has a lifetime community prevalence of about 4%,2 which is approximately one-quarter of the prevalence of unipolar major depressive disorder.3 About 1% of the population has bipolar I disorder (most often severe mood elevations, as well as depressive episodes), 1% has bipolar II disorder (mild-to-moderate mood elevations, as well as depressive episodes), and about 2% have either cyclothymia (chronic recurrent mild mood disturbances) or bipolar disorder NOS (meet some criteria for a bipolar condition but not full criteria for either bipolar I or bipolar II disorder).

Race and ethnicity have no effect on prevalence rates in community samples,2 although evidence4 suggests that some selection bias may occur in clinical settings. Gender has no overall effect on community prevalence rates,2,5 but women appear to have a greater risk for rapid cycling compared to men.6 Patients with mixed rather than pure euphoric mania/hypomania may be more likely to be female.7 In comparison to men, women also have fewer hypomanic and more depressive episodes8 and are more likely to experience depression during hypomania.9 The peak mean age at onset for all bipolar disorders ranges from late adolescence to early adulthood,2 with more than two-thirds of patients experiencing onset prior to age 18 years.5,10

Impact of Bipolar Disorder

The impact of bipolar disorder can be observed across several aspects of patients’ lives. Depressive symptoms compared to mood elevation symptoms are more pervasive and appear to yield more functional impairment. In a study2 of patients with diagnoses across the spectrum of bipolar disorders, 87% of patients who had experienced a depressive episode in the previous year reported severe role impairment (with respect to work, social life, leisure activities, and family and home responsibilities) compared with 57% of those who had experienced a manic or hypomanic episode in the previous year. In view of the generally early age of onset, bipolar disorder commonly undermines social, educational, and early career development, which may explain why bipolar disorder is associated with lower educational levels and higher rates of unemployment than the general population.2 Indeed, an epidemiologic study11 found that individuals with bipolar disorder compared with those without were significantly more likely to have ever been fired or laid off; to have had a supervisor unhappy with their work, behavior, or attitudes; and to have had interactions with the criminal justice system (P < .0001, AV 1AV 1).

Bipolar disorder is associated with increased rates of comorbid psychiatric and medical disorders, which can complicate the diagnosis, course, and treatment. In one study,12 65% of patients with bipolar disorder had 1 or more lifetime comorbid Axis I diagnoses, while more than 40% of patients had 2 or more, and almost 25% had 3 or more. The most common psychiatric comorbidities were anxiety and substance use disorders, while common medical comorbidities included cardiovascular disease and obesity (AV 2AV 2).12,13

In 2000, the World Health Organization estimated that bipolar disorder was the fifth leading cause of years lived with disability for individuals aged 15 years to 44 years and the ninth leading cause of years lived with disability among people of all ages.14 Bipolar disorder is associated with increased rates of mortality from “natural” causes such as cardiovascular disease, cerebrovascular disease, gastrointestinal disorders, and endocrine disorders like diabetes. Death from “natural” causes may account for approximately half of the excess mortality seen in patients with bipolar disorder; the other half is due to increased mortality from “unnatural” causes such as suicide, homicide, or accidents.15 As many as 50% of patients with bipolar disorder may attempt suicide, and completed suicides may be as high as 25% early in the illness course.16,17


Patients with bipolar disorder are high users of health care in both primary care and psychiatric settings. In a national survey,2 about 90% of patients with bipolar I disorder and 95% of patients with bipolar II disorder reported seeking treatment for emotional problems, usually from psychiatrists, and approximately 70% of patients with subthreshold bipolar disorder had sought treatment for emotional problems, usually from general medical professionals. One study18 estimated that the lifetime direct and indirect costs of treating a patient with treatment-refractory bipolar disorder (with an onset in 1998) could exceed $600,000 (in 1998 US dollars, AV 3AV 3). The total annual cost of bipolar disorder to the entire US economy was estimated to be approximately $45 billion, using prevalence-based cost-of-illness data from 1991. Direct treatment costs only accounted for less than 20% of this amount, while indirect costs—eg, excess unemployment, lowered productivity, and excess mortality from suicide—accounted for most of the cost. Intangible and certain indirect costs such as quality of life issues or the value of uncompensated care from family members were not included.

For Clinical Use

  • In bipolar disorder, mood elevation is the defining characteristic, but depression is more pervasive
  • Bipolar disorder in its broadest sense has a lifetime community prevalence rate of approximately 4%
  • Bipolar disorder is a severely impairing illness that impacts several aspects of patients’ lives
  • Direct and indirect costs for treating bipolar disorder may be comparable or even exceed those for unipolar depressive disorder, despite the latter being approximately 4 times as prevalent


ADHD = attention-deficit/hyperactivity disorder
DSM-IV-TR = Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision
NOS = not otherwise specified

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