Bipolar Disorder: A High-Yield USMLE Review

Bipolar disorder is a mood disorder defined by the presence of mania (Bipolar I) or hypomania (Bipolar II). It is one of the most heavily tested psychiatric concepts because the distinction from major depressive disorder hinges entirely on the history of a manic or hypomanic episode—and because mismanagement (antidepressant monotherapy) can trigger mania. Mood stabilizers are the foundation of treatment.

Presentation

• Manic episode: decreased need for sleep with sustained high energy (e.g., sleeping only ~2 hours a night yet feeling 'full of energy')
• Grandiosity and impulsive, high-risk behavior (quitting a job to start a 'million-dollar business,' maxing out credit cards, impulsive spending of tuition money)
• Rapid/pressured speech and irritability, especially when interrupted
• Bipolar depression: a depressive episode occurring in a patient with a past manic or hypomanic episode (clinically indistinguishable from unipolar depression except for that history)
• Often a first presentation in young adults, frequently with a family history of bipolar disorder

Diagnosis

• Longitudinal mood history is the diagnostic instrument: definitively establishing bipolar disorder requires documenting a prior manic or hypomanic episode—a single depressive presentation can only be labeled 'no documented mania so far'
• Collateral history from family/roommates to capture hypomanic episodes the patient may not report; family history of bipolar disorder is a Bayesian prior that raises but does not establish the diagnosis
• Basic medical screen (vital signs, glucose, electrolytes, TSH, CBC/CMP) and substance screening to exclude medical mimics and substance-precipitated mania before committing to a primary psychiatric diagnosis

Management

• Acute mania: first-line is a mood stabilizer (lithium or valproate) and/or an atypical antipsychotic (olanzapine, risperidone, quetiapine, aripiprazole); rapid stabilization plus a higher level of care than routine outpatient follow-up given perpetuating factors like ongoing sleep loss
• Bipolar depression requires mood stabilizers—not antidepressant monotherapy; mood stabilizers are the foundation of treatment and are typically maintained indefinitely
• Monitor long-term lithium therapy with renal and thyroid function testing

High-yield

• Bipolar disorder is DEFINED by mania (Bipolar I) or hypomania (Bipolar II)—the depressive episodes look identical to MDD
• A depressive episode with NO history of mania = MDD; a depressive episode WITH past mania = bipolar depression
• Always ask about mania/hypomania before starting an antidepressant—antidepressant monotherapy can trigger a manic switch
• Sleep deprivation is a perpetuating biological driver of mania—continued sleep loss worsens the episode
• Mood stabilizers are typically maintained indefinitely in bipolar disorder
• A substantial fraction of patients initially diagnosed with MDD are later found to be bipolar when followed prospectively

Pitfalls

• Starting an SSRI/antidepressant as monotherapy in an unrecognized bipolar patient—this can precipitate mania; screen for prior hypomania and counsel about manic warning signs first
• Anchoring on a prior diagnosis of recurrent unipolar depression: apparent 'treatment-resistant depression' (loss of response to a previously effective SSRI) may actually be undiagnosed bipolar disorder, a new medical contributor, or covert substance use
• Diagnostic overshadowing: attributing new symptoms in a patient with known bipolar disorder to their psychiatric illness without a medical workup—patients with severe mental illness have high rates of medical comorbidity
• Confusing a first manic presentation with stimulant intoxication or dismissing it—continued spending and sleep loss compound harm hourly and demand urgent stabilization