Bit · Behavioral
Mood Disorders — MDD vs Persistent Depressive vs Bipolar I/II
Four core mood disorders. The pivot is whether there has been a manic or hypomanic episode, and how long the depression has lasted.
Mechanism
Mood disorders split first on whether there is a history of mania/hypomania (bipolar spectrum) or not (depressive spectrum):
- Major depressive disorder (MDD) — ≥ 1 major depressive episode (≥ 5 of 9 SIGECAPS symptoms for ≥ 2 weeks, with at least one being depressed mood or anhedonia). No history of mania or hypomania.
- Persistent depressive disorder (dysthymia) — depressed mood most of the day, more days than not, for ≥ 2 years (≥ 1 year in children/adolescents). Less severe but more chronic than MDD.
- Bipolar I — at least one full MANIC episode (≥ 7 days, or any duration requiring hospitalisation). Depressive episodes may occur but are NOT required for diagnosis.
- Bipolar II — at least one HYPOmanic episode (≥ 4 days) PLUS at least one major depressive episode. Never had a full manic episode.
- Cyclothymia — fluctuating hypomanic and depressive symptoms for ≥ 2 years that don't meet full criteria for either.
SIGECAPS: Sleep, Interest, Guilt, Energy, Concentration, Appetite, Psychomotor, Suicidality.
Mania (DIGFAST): Distractibility, Indiscretion (risky behaviour), Grandiosity, Flight of ideas, Activity increase, Sleep need decreased, Talkativeness.
Differentiator Table
| Disorder | Required episodes | Duration | Treatment |
|---|---|---|---|
| MDD | Major depressive episode | ≥ 2 weeks | SSRI / SNRI; CBT; ECT in refractory or psychotic depression |
| Persistent depressive (dysthymia) | Depressed mood most days | ≥ 2 yrs (1 in adolescents) | SSRI + psychotherapy |
| Bipolar I | At least 1 MANIC episode | ≥ 7 days (or hospitalisation) | Lithium, valproate, antipsychotics; AVOID antidepressants alone |
| Bipolar II | ≥ 1 hypomanic + ≥ 1 MDE | Hypomania ≥ 4 days | Mood stabilisers; cautious antidepressants with mood stabiliser cover |
| Cyclothymia | Subthreshold hypomania + depressive symptoms | ≥ 2 yrs | Mood stabilisers |
The Pivot
Two questions:
- Has the patient ever had mania or hypomania? Yes, full mania → bipolar I. Yes, hypomania + a depressive episode → bipolar II. Subthreshold cycling → cyclothymia. No → depressive spectrum.
- If depressive — how long? ≥ 2 weeks of full criteria → MDD. ≥ 2 years of low-grade chronic depression → dysthymia.
Trap: never start an antidepressant alone in suspected bipolar — it can precipitate mania.
NBME-Style Stem
A 24-year-old man is brought in by his family for 5 days of decreased need for sleep, racing thoughts, grandiose plans to start a music label, and reckless spending of $40,000 on credit cards. He has been hospitalized for similar behaviour twice before. Between episodes he is euthymic or mildly depressed. Which of the following is the most likely diagnosis?
Concept Anchor
Mood disorders are first split by whether mania has ever happened. Bipolar = one full manic episode (or hypomanic + depressive). Depressive spectrum = no mania. Duration cuts MDD (≥ 2 weeks) from dysthymia (≥ 2 years).