Bipolar I Disorder

Bipolar I disorder is the form of bipolar disorder defined by the occurrence of at least one full manic episode. Depressive and hypomanic episodes commonly occur as well, but a single lifetime manic episode is sufficient for the diagnosis, which distinguishes bipolar I from the other disorders on the bipolar spectrum.

Definition

Bipolar I disorder is a mood disorder diagnosed when a person has experienced at least one manic episode; major depressive and hypomanic episodes are common but are not required for the diagnosis.

Scope

This entry covers the defining requirement of a manic episode, the features that separate bipolar I from bipolar II and from unipolar depression, its epidemiology and course, and the general principles of how the diagnosis is framed. It is reference material describing the diagnostic concept, not clinical guidance.

Core questions

• What clinical features constitute a manic episode sufficient to diagnose bipolar I disorder?
• How does bipolar I differ from bipolar II disorder and from major depressive disorder?
• What is the typical age of onset, course, and prognosis of bipolar I disorder?

Key concepts

• Manic episode (diagnostic anchor)
• Psychotic features in mania
• Mixed features
• Rapid cycling
• Recurrence and relapse
• Functional impairment

Mechanisms

The diagnostic anchor of bipolar I disorder is the manic episode: a distinct period of abnormally elevated, expansive, or irritable mood with persistently increased activity or energy, lasting at least about a week (or any duration if hospitalisation is required), accompanied by features such as inflated self-esteem, decreased need for sleep, pressured speech, racing thoughts, distractibility, increased goal-directed activity, and risky behaviour. The episode causes marked impairment and may include psychotic symptoms. Because one manic episode defines the disorder, bipolar I is separated from bipolar II (in which only hypomania, never mania, has occurred) and from unipolar depression (in which no manic or hypomanic pole exists).

Clinical relevance

Bipolar I disorder is associated with substantial functional disability, recurrent episodes, elevated suicide risk, and frequent psychiatric and medical comorbidity. Recognising the manic pole is central to distinguishing it from unipolar depression in research and education. This entry describes the diagnostic concept and is not a basis for individual diagnosis or treatment.

Epidemiology

Population surveys estimate the lifetime prevalence of bipolar I disorder at roughly 0.6 to 1 percent, with onset most often in late adolescence or early adulthood and a broadly equal distribution between men and women; the lifetime prevalence of the wider bipolar spectrum is several percent (Merikangas and colleagues 2007).

Evidence & guidelines

Reviews by Grande and colleagues (2016), Carvalho and colleagues (2020), and Vieta and colleagues (2018) summarise the diagnosis, neurobiology, and course of bipolar I disorder. The diagnostic criteria follow DSM-5 (bipolar I) and ICD-11 (category 6A60).

History

Bipolar I disorder is the direct descendant of Kraepelin's manic-depressive insanity. The explicit separation of bipolar from unipolar depression in the later twentieth century, and the subdivision into bipolar I and bipolar II in DSM-IV and DSM-5, gave the manic episode its present role as the defining feature of the type I disorder.

Debates

Where should the boundary between bipolar I and the rest of the spectrum lie?

Whether the categorical bipolar I / bipolar II / cyclothymia distinctions best capture a condition that may be dimensional remains debated, with implications for case definition, prevalence estimates, and research comparability.

Key figures

• Emil Kraepelin
• Eduard Vieta
• Kathleen Merikangas
• Boris Birmaher

Seminal works

• grande-2016
• merikangas-2007
• carvalho-2020

Frequently asked questions

Does a person need to have been depressed to be diagnosed with bipolar I disorder?

No. A single lifetime manic episode is sufficient for the diagnosis of bipolar I disorder; depressive episodes are common but are not required.

What separates bipolar I from bipolar II disorder?

Bipolar I requires at least one full manic episode, whereas bipolar II is defined by hypomanic and major depressive episodes without any history of full mania.