Can a Patient with Bipolar II Disorder Also Be Diagnosed with Major Depressive Disorder?
No, a patient cannot simultaneously carry both diagnoses of Bipolar II Disorder and Major Depressive Disorder—these are mutually exclusive diagnostic categories. Once a patient meets criteria for Bipolar II Disorder (at least one hypomanic episode plus at least one major depressive episode), the diagnosis supersedes any prior MDD diagnosis 1, 2.
Why These Diagnoses Are Mutually Exclusive
The DSM-5 explicitly separates depressive disorders from bipolar and related disorders as distinct diagnostic categories 1. This structural separation in the diagnostic manual reflects the fundamental understanding that these represent different illness trajectories requiring different treatment approaches.
Bipolar II Disorder is defined by the presence of at least one major depressive episode AND at least one hypomanic episode, with no history of full manic episodes 2. The occurrence of even a single hypomanic episode fundamentally changes the diagnostic classification from MDD to Bipolar II Disorder.
The diagnostic hierarchy places bipolar disorders above unipolar depression—meaning that once bipolarity is established through documented hypomania, the patient's depressive episodes are understood as part of the bipolar illness course, not as a separate MDD diagnosis 3, 4.
The Clinical Reality: Misdiagnosis Is Common
Bipolar II Disorder is frequently misdiagnosed as MDD because patients with BD-II present with recurrent depressive episodes that outnumber hypomanic episodes by a ratio of 39:1 4. Patients typically seek treatment during depressive phases, while hypomanic episodes may go unrecognized or unreported.
Without proper screening and comprehensive evaluation, many patients with bipolar disorder are misdiagnosed with MDD 5. This represents diagnostic error rather than dual diagnosis—the patient had Bipolar II Disorder all along, but it was incorrectly labeled as MDD.
Approximately 20% of youths initially diagnosed with major depression eventually develop manic or hypomanic episodes, revealing the underlying bipolar nature of their illness 2, 6. This conversion demonstrates that the initial MDD diagnosis was incomplete or premature.
Critical Diagnostic Distinctions
The key assessment requires asking specifically about distinct periods of abnormally elevated, expansive, or irritable mood that represented a marked departure from baseline functioning, with symptoms evident across different realms of life 3. This screening question is essential to differentiate between the two conditions.
Antidepressant-induced mood elevation or agitation strongly suggests underlying bipolarity, with the risk of antidepressant-associated mood elevations being 2.77 times higher in Bipolar II Disorder compared to MDD 2, 7. This treatment response pattern serves as a critical diagnostic clue.
Earlier age of depression onset (typically before age 25), family history of bipolar disorder in first-degree relatives (4-6 fold increased risk), and presence of atypical depressive features all favor Bipolar II Disorder over MDD 2, 3, 8.
Why This Distinction Matters Clinically
Antidepressant monotherapy is contraindicated in bipolar depression and must be combined with a mood stabilizer if used at all 2, 6. Treating Bipolar II Disorder as if it were MDD with antidepressants alone can worsen the prognosis and potentially induce mood destabilization.
Quetiapine or lamotrigine are first-line treatments for bipolar depression, while lithium has strong long-term evidence for maintenance treatment 2, 6. These treatment approaches differ fundamentally from MDD management.
Bipolar II Disorder carries substantially higher suicide risk than MDD, with lifetime suicide attempt prevalence of 29.2% in bipolar disorder versus 5.6% in MDD, and an 8.66-fold increased risk of completed suicide compared to the general population 1, 3. This elevated risk necessitates more intensive monitoring and different safety planning.
Common Pitfall to Avoid
The most dangerous clinical error is maintaining an MDD diagnosis after hypomanic episodes have been identified, or failing to systematically screen for hypomania in patients presenting with depression. Always obtain collateral history from family members about observed mood changes, as patients often lack insight into hypomanic episodes or may view them positively 3. Document the longitudinal course using a life chart to map mood episodes chronologically, which often reveals the bipolar pattern that cross-sectional assessment misses 3.