ICD-116A61	BIPOLAR TYPE II DISORDER Bipolar type II disorder
ICD-10F31	Bipolar affective disorder
DSM-5-TRF31.81	Bipolar II Disorder

1. Definition and nosology

Bipolar disorder Type II (ICD-11: 6A61; DSM-5-TR: F31.81) — a form of bipolar disorder characterized by at least one hypomanic episode and at least one major depressive episode, but never a full manic episode. It is not a ‘milder’ form than Type I — patients spend more lifetime time in depression; functional impairment and suicide risk are comparable to Type I.

2. History

• Dunner D.L., Gershon E.S., Goodwin F.K. (1976) — proposal to differentiate bipolar disorder subtypes.
• DSM-IV (1994) — Bipolar Type II as a separate diagnostic category formalized.
• DSM-5 (2013) and ICD-11 (2019) — Type II retained, with emphasis against the erroneous concept of it as a ‘mild form’.

3. Epidemiology

• Lifetime prevalence: ~0.4–1.1% (Merikangas K.R. Arch Gen Psychiatry 2011 WMH).
• Sex: relatively higher in females (~1.5:1 — different from Type I).
• Onset: mid-20s to 25 years; multiple depressive episodes usually precede a hypomanic episode.
• Suicide risk comparable to Type I (lifetime ~5–7%); more often due to depressive episodes.
• Comorbidity: anxiety 60%+, substance use 30–40%, borderline personality disorder.

4. Aetiology and pathogenesis

• Genetic basis overlaps with Type I — heritability 60–80%; GWAS loci parallel.
• Genetic independence of the clinical phenotype from bipolar Type I is debated — some studies assess both types as the same spectrum.
• Circadian rhythm disturbance and family history.

5. Clinical features

5.1 Hypomanic episode

• Abnormally elevated or irritable mood + increased energy ≥ 4 days (≥ 7 in Type I).
• Same sub-symptoms as manic episode (decreased need for sleep, distractibility, increase in goal-directed activity, etc.); ≥ 3 symptoms (≥ 4 if irritable mood).
• Functional impairment should not be significant (i.e., hypomanic definition); no psychotic features; no hospitalization required. If these criteria are observed — diagnosis changes to Type I.

5.2 Major depressive episode

• ≥ 5 symptoms for 2 weeks (including low mood and/or anhedonia).
• Bipolar Type II depressive episodes often with atypical features — hypersomnia, hyperphagia, leaden paralysis, rejection sensitivity.
• Patients are symptomatic during 53.9% of follow-up weeks; depressive symptoms occupy 50.3% of weeks (hypomanic 1.3%, cycling/mixed 2.3%) — Judd L.L. et al. Arch Gen Psychiatry 2003, n=86, mean 13.4 years of follow-up; most symptoms are at subsyndromal level.

6. Diagnosis

6.1 Unified diagnostic criteria

A. At least one hypomanic episode.

B. At least one major depressive episode.

C. Never had a manic episode.

D. Hypomanic and depressive episodes are not better explained by schizoaffective disorder, schizophrenia, or another psychotic disorder.

E. Symptoms cause significant distress or functional impairment (primarily from depressive episode).

6.2 Source-specific clarifications

• DSM-5-TR / ICD-11: functional impairment in hypomanic episode should not be significant; antidepressant-induced hypomanic episode leads to bipolar Type II diagnosis (especially in persistent or recurrent cases).
• Underdiagnosis problem: Hirschfeld R.M. reviews — ~25–50% of patients presenting with a depressive episode are actually Bipolar Type II, but hypomanic episodes are perceived by the family as “good periods.”

6.3 Diagnostic algorithm

1. Structured inquiry for hypomanic episodes in every depressive patient (SCID-5 mood module, MDQ, HCL-32).
2. Information from family members — observation of hypomanic episodes is important.
3. Clinical interview + YMRS, HAM-D / MADRS.
4. Laboratory: thyroid, liver, kidney, toxicology, pregnancy test.
5. Comorbidity and suicide risk assessment.

6.4 Differential diagnosis

7. Examination and assessment

• SCID-5 mood module — the gold standard.
• MDQ (Mood Disorder Questionnaire) and HCL-32 (Hypomania Checklist) — screening.
• YMRS, HAM-D / MADRS, C-SSRS.
• Pre-lithium: creatinine, TSH, calcium, EKG.

8. Treatment

8.1 General principles (NICE CG185 · CANMAT/ISBD 2018)

1. Bipolar Type II depressive episode (most common presentation):
   • First-line — quetiapine (FDA approved) or quetiapine + lithium combination. Lurasidone's FDA indication covers bipolar I depression only, not type II; CANMAT/ISBD 2018 likewise names quetiapine alone as first-line for the type II depressive episode.
   • Lamotrigine — first-line in maintenance and depressive prophylaxis (particularly effective in Type II).
   • Lithium — maintenance and suicide reduction.
2. Hypomanic episode: Stop antidepressant; mood stabilizer (lithium, valproate) or atypical antipsychotic.
3. Antidepressant use: formerly considered relatively safe in bipolar Type II, but recent guidelines (CANMAT 2018) recommend only with a mood stabilizer (to reduce risk of manic switch and rapid cycling).
4. Maintenance: Lamotrigine (when the depressive component is dominant) or quetiapine; lithium for suicide reduction effect.
5. Psychosocial: CBT, IPSRT, family-focused therapy, psychoeducation.
6. Refractory: clozapine, ECT.
7. Pregnancy: valproate absolute contraindication; lamotrigine and quetiapine relatively safe.

8.2 Source-specific clarifications

• CANMAT/ISBD 2018: Type II depressive episode first-line — quetiapine; lamotrigine in maintenance.
• NICE CG185: Type I and II same main approach, but lamotrigine's specific role emphasized in Type II.
• Calabrese J.R. RCTs — lamotrigine efficacy in maintenance treatment of bipolar disorder type II.

Treatment methods

1. Lamotrigine — Bipolar Type II effective in maintenance and prevention of depressive episodes; titration slow (risk of Stevens-Johnson syndrome) — starting dose 25 mg, increase over 2 weeks; target 200 mg/day. Calabrese J.R. et al. J Clin Psychiatry 2003.
2. Quetiapine — FDA approval for bipolar depressive episode; 300–600 mg/day; metabolic side effect monitoring.
3. Interpersonal and Social Rhythm Therapy (IPSRT) — Frank (Frank E.); and CBT for bipolar disorder — Circadian rhythm, compliance, relapse prevention.
4. Hypomania Checklist (HCL-32) — Angst J — 32-item self-assessment hypomanic episode screening.
5. Mood Disorder Questionnaire (MDQ — Mood Disorder Questionnaire) — 13 questions; bipolar screening.

9. Prognosis

• Episodic course; relapse significantly reduced with maintenance pharmacotherapy.
• Type II is not ‘milder’ than Type I — high functional impairment and depressive burden.
• Suicide risk high.
• Quetiapine and lamotrigine in maintenance as main.
• Monitoring — depressive symptoms, hypomanic triggers, metabolic indicators.

10. Myths and misconceptions

Myth 1: “Type II bipolar is a ‘mild form’ requiring little treatment”

Evidence: Judd L.L. Arch Gen Psychiatry 2003 — Type II patients spend 50.3% of follow-up weeks with depressive symptoms (53.9% symptomatic overall); functional impairment and suicide risk comparable to Type I.

Myth 2: “Hypomanic episode is a ‘good period’, no treatment needed”

Evidence: hypomanic episode can involve risky behavior, impaired relationships, later productivity decline, and trigger depressive episode; isolated episodes indicate need for maintenance pharmacotherapy.

Myth 3: “Antidepressant alone can be used in Type II patient”

Evidence: CANMAT 2018 — antidepressant only with mood stabilizer; risk of manic switch and rapid cycling.

Myth 4: “Bipolar Type II is only a form of borderline personality disorder”

Evidence: There is significant overlap and comorbidity, but these are distinct disorders; bipolar Type II episodic, BPD continuous pattern.

Myth 5: “Lamotrigine cures a manic episode”

Evidence: Lamotrigine is effective in the depressive component and maintenance; ineffective for manic episodes — antipsychotic or valproate is required.

Myth 6: “St John's Wort is safe in bipolar because it is a natural antidepressant”

Evidence: St. John's Wort can induce mania and decrease the levels of mood stabilizers (CYP induction); contraindicated in bipolar disorder.

Myth 7: ECT is not needed in Type II

Evidence: ECT indicated for refractory depressive episode or high suicidality risk; also effective in Type II patient.

11. Sources

1. WHO. ICD-11. 6A61 Bipolar type II disorder. 2024.
2. APA. DSM-5-TR. 2022.
3. NICE CG185. 2014/2020.
4. Yatham L.N. et al. CANMAT and ISBD 2018 guidelines. Bipolar Disord 2018;20(2):97–170.
5. Judd L.L., Akiskal H.S., Schettler P.J. et al. A prospective investigation of the natural history of the long-term weekly symptomatic status of bipolar II disorder. Arch Gen Psychiatry 2003;60(3):261–269.
6. Calabrese J.R. et al. A placebo-controlled 18-month trial of lamotrigine and lithium maintenance treatment in recently depressed patients with bipolar I disorder. J Clin Psychiatry 2003;64(9):1013–1024.
7. Cipriani A. et al. BMJ 2013;346:f3646.
8. Merikangas K.R. et al. Arch Gen Psychiatry 2011;68(3):241–251.
9. Angst J. et al. The HCL-32: towards a self-assessment tool for hypomanic symptoms. J Affect Disord 2005;88(2):217–233.
10. Hirschfeld R.M., Williams J.B., Spitzer R.L. et al. Development and validation of a screening instrument for bipolar spectrum disorder: the Mood Disorder Questionnaire. Am J Psychiatry 2000;157(11):1873–1875.
11. Frank E., Kupfer D.J., Thase M.E. et al. Two-year outcomes for interpersonal and social rhythm therapy in individuals with bipolar I disorder. Arch Gen Psychiatry 2005;62(9):996–1004.