2. Mood Disorders

This page is for educational purposes. Always verify with current clinical guidelines.

Learning Objectives

• Apply DSM-5 criteria to diagnose major depressive disorder (MDD), persistent depressive disorder, bipolar I, bipolar II, and cyclothymic disorder
• Distinguish mania from hypomania and explain why that distinction determines whether a patient is bipolar I or bipolar II
• Describe the monoamine hypothesis of mood regulation and how SSRIs, SNRIs, and mood stabilizers act on it
• Recognize red flags — suicidality, psychotic features, mixed features — that change management urgency
• Compare first-line pharmacologic and psychotherapeutic treatments across the mood disorder spectrum
• Explain why screening for hypomania/mania is mandatory before starting an antidepressant for depression

Quick Answer

Mood disorders are a group of psychiatric conditions defined by a sustained disturbance in emotional state that impairs functioning — not just a bad week. The spectrum runs from unipolar depression (major depressive disorder, persistent depressive disorder) to bipolar disorders, where mood swings between depression and mania or hypomania. They matter because depression is a leading cause of disability worldwide and bipolar disorder carries among the highest suicide risk of any psychiatric illness. The core clinical skill is pattern recognition: how long symptoms last, how severe they are, and — critically — whether the patient has ever had a manic or hypomanic episode, because missing a bipolar history and starting an unopposed antidepressant can trigger a manic switch.

Core Concepts

Major Depressive Disorder (MDD)

Definition: MDD is diagnosed when a patient has at least 5 of 9 DSM-5 symptoms for at least 2 weeks, with at least one being depressed mood or anhedonia (loss of interest/pleasure), causing significant functional impairment.

Explanation: The mnemonic SIG E CAPS captures the 9 criteria: Sleep changes, Interest loss (anhedonia), Guilt/worthlessness, Energy loss, Concentration difficulty, Appetite/weight change, Psychomotor agitation or retardation, Suicidal ideation, and depressed mood. You need 5 of these 9, present nearly every day, and one of the 5 must be depressed mood or anhedonia — you cannot diagnose MDD in someone who sleeps poorly, has lost weight, and feels guilty but never reports low mood or loss of interest.

Example: A patient reports 3 weeks of waking at 4 a.m. unable to fall back asleep, no longer enjoying weekend hobbies, poor concentration at work, and feeling like a burden to their family — that's depressed mood/anhedonia plus sleep, concentration, and guilt: 4-5 criteria, easily meeting threshold.

Real-World Example: Sarah, a 28-year-old marketing specialist, developed MDD after losing her mother to cancer. She described persistent emptiness, lost interest in her job, and early-morning awakening. This is a textbook grief-triggered depressive episode — normal grief and MDD can look similar, but MDD is diagnosed when symptoms are pervasive, functionally disabling, and persist well beyond what is culturally expected for bereavement.

Why It Matters: MDD is a leading global cause of disability (WHO data) and roughly doubles the risk of medical comorbidities like cardiovascular disease. Every depressed patient must be screened for suicidal ideation — this is the single highest-yield safety step in psychiatry.

Common Misunderstanding: Students often think sadness alone equals MDD. In reality, MDD requires functional impairment and a specific symptom count/duration — situational sadness that resolves in days, without the other criteria, is not a diagnosis.

Bipolar I and Bipolar II Disorder

Definition: Bipolar I requires at least one manic episode (≥1 week, or any duration if hospitalization is needed); depressive episodes are common but not required for diagnosis. Bipolar II requires at least one hypomanic episode (≥4 days) plus at least one major depressive episode — a full manic episode would upgrade the diagnosis to Bipolar I.

Explanation: The key distinguishing feature between mania and hypomania is severity, not symptoms — both share the mnemonic DIG FAST: Distractibility, Irresponsibility (risky behavior — spending sprees, sexual indiscretion), Grandiosity, Flight of ideas, Activity increase, Sleep need decreased, Talkativeness/pressured speech. Mania causes marked impairment, may include psychotic features, and often requires hospitalization. Hypomania is noticeable to others but does NOT cause marked impairment and never includes psychosis — the patient can still function, just "more" than usual.

Example: A patient who hasn't slept in 4 days, is convinced they've solved climate change, has spent their life savings on a business idea overnight, and is talking so fast you can't interrupt them — that's mania, meeting Bipolar I criteria. If instead they just seem unusually energetic, chatty, and productive for 5 days without derailing their life, that's hypomania — Bipolar II territory.

Real-World Example: John, a 35-year-old software engineer, was diagnosed with Bipolar II. He had recurrent depressive episodes and shorter stretches of elevated mood and reduced sleep that boosted his productivity without causing catastrophic decisions — a pattern many Bipolar II patients don't recognize as pathological because the hypomanic periods can feel good.

Why It Matters: Bipolar disorder has one of the highest lifetime suicide rates in psychiatry (up to 15-20x general population in some studies), largely during depressive or mixed episodes. It's also frequently misdiagnosed as unipolar depression when patients present only during a depressive episode and don't volunteer a manic/hypomanic history.

Common Misunderstanding: Many assume "bipolar" always means dramatic, obvious mood swings. Bipolar II's hypomania is subtle and easy to miss on history — always ask directly about periods of decreased sleep need, elevated mood, or unusual productivity/impulsivity.

Cyclothymic Disorder and Persistent Depressive Disorder (Dysthymia)

Definition: Cyclothymic disorder involves numerous periods of hypomanic and depressive symptoms that don't meet full criteria for hypomania or MDD, present for at least 2 years (1 year in children/adolescents) without a symptom-free period longer than 2 months. Persistent depressive disorder (dysthymia) is chronic, low-grade depressive symptoms lasting at least 2 years (1 year in children) that may not meet full MDD criteria at any point, though a "double depression" (dysthymia plus a superimposed MDD episode) is common.

Explanation: Think of these as the chronic, lower-amplitude cousins of bipolar disorder and MDD respectively. The defining feature is duration and persistence rather than episode severity — patients live with a "baseline" mood disturbance rather than distinct episodes.

Example: A patient who describes "always being the moody one" since college, with fluctuating good and bad stretches that never quite reach mania or full depression, fits cyclothymia. A patient who has felt "low-grade down" for 3 years, functioning but never really happy, fits dysthymia.

Real-World Example: Emily, a 22-year-old artist, struggled with cyclothymic disorder through college — mood swings affected her ability to finish projects, though she never had a full manic or major depressive episode. David, a 40-year-old accountant, lived with dysthymia for over five years, gradually improving with therapy and antidepressants.

Why It Matters: Because symptoms are chronic rather than acute, patients and clinicians often normalize them as "personality" rather than a treatable illness — leading to years of untreated impairment before diagnosis.

Common Misunderstanding: Students often assume these are "mild" and don't need treatment. In practice, chronic subthreshold symptoms cause substantial cumulative functional impairment and respond to the same treatments (psychotherapy, medication) as their more acute counterparts.

Visual Learning

Neurobiology of Mood Regulation

Mood disorders arise from disrupted monoamine signaling and structural/functional changes in mood-regulating circuits — this is the biological basis for why medications work.

• Serotonin: Regulates mood, appetite, and sleep; the primary target of SSRIs
• Norepinephrine: Affects arousal, energy, and stress response; targeted by SNRIs and TCAs
• Dopamine: Drives reward and motivation; anhedonia in depression reflects blunted dopaminergic reward signaling
• Prefrontal cortex: Executive function and mood regulation — often shows reduced activity in depression
• Amygdala: Emotional processing, especially fear/threat; often hyperactive in depression and anxiety
• Hippocampus: Memory and stress-response regulation; chronic cortisol exposure in depression is linked to hippocampal volume reduction

This is often called the "monoamine hypothesis," but it's a simplification — it explains why boosting serotonin/norepinephrine helps many patients, but it doesn't fully explain why antidepressants take weeks to work (implicating downstream neuroplasticity changes) or why some patients don't respond at all.

Real-World Applications

Correctly classifying mood disorders isn't academic — it drives treatment choice and prevents harm. Starting an SSRI in an undiagnosed bipolar patient without a mood stabilizer can precipitate a manic switch or rapid cycling. Recognizing suicidality risk stratifies who needs emergency evaluation versus outpatient follow-up. Primary care physicians manage the majority of depression cases, so accurate screening (e.g., PHQ-9) and referral thresholds are essential generalist skills, not just psychiatric subspecialty knowledge.

Common Mistakes

Misconception: Any mood swing or irritability means someone is "bipolar." Why it's wrong: Bipolar disorder requires a documented episode of mania or hypomania meeting specific duration and symptom criteria — not general moodiness, irritability, or normal emotional reactivity to stress. Correct understanding: Bipolar diagnosis requires DIG FAST criteria sustained for ≥4 days (hypomania) or ≥1 week/hospitalization (mania), with clear functional change from the patient's baseline.

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Misconception: It's safe to start any antidepressant as soon as a patient reports depressive symptoms. Why it's wrong: If the patient has undiagnosed bipolar disorder, an antidepressant given without a mood stabilizer can trigger a manic episode or accelerate cycling between mood states. Correct understanding: Always screen for any personal or family history of mania/hypomania before starting antidepressant monotherapy; if bipolar disorder is suspected, mood stabilizers or antipsychotics are first-line, not antidepressants alone.

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Misconception: Dysthymia and cyclothymia are minor conditions that don't need active treatment. Why it's wrong: Both are chronic (≥2 years) and cause real, cumulative functional impairment, and both carry risk of progression to more severe episodes ("double depression" or full bipolar disorder). Correct understanding: These conditions warrant the same treatment approach — psychotherapy and/or pharmacotherapy — as their acute counterparts, adjusted for chronicity.

Comparison and Connections

Feature	Major Depressive Disorder	Bipolar I Disorder	Bipolar II Disorder
Defining episode	Depressive episode only	At least one manic episode	Hypomanic + depressive episode(s)
Episode duration	≥2 weeks depressive symptoms	≥1 week mania (or any duration if hospitalized)	≥4 days hypomania
Psychotic features possible	Yes (severe MDD with psychotic features)	Yes, during mania	No (would reclassify as Bipolar I)
First-line medication	SSRIs/SNRIs	Mood stabilizers (lithium, valproate) ± antipsychotics	Mood stabilizers; antidepressants used cautiously
Key risk if mismanaged	Untreated suicidality	Manic relapse, psychiatric hospitalization	Missed diagnosis if only depression is seen

Practice Questions

Recall

1. What is the SIGECAPS mnemonic used for, and how many of the 9 criteria are needed for an MDD diagnosis? Guidance: SIGECAPS lists the 9 DSM-5 symptom domains for MDD (Sleep, Interest, Guilt, Energy, Concentration, Appetite, Psychomotor change, Suicidality, depressed mood). At least 5 of 9 must be present for 2 weeks, including depressed mood or anhedonia.

2. What is the minimum duration required to diagnose a manic episode versus a hypomanic episode? Guidance: Mania requires ≥1 week (or any duration if hospitalization is needed); hypomania requires ≥4 days.

Understanding

3. Why does Bipolar II require a major depressive episode for diagnosis, while Bipolar I does not? Guidance: Bipolar I is defined solely by the occurrence of a manic episode, regardless of whether depression ever occurs. Bipolar II specifically requires both a hypomanic episode and at least one major depressive episode — a patient with only hypomania and no depressive episode would not meet Bipolar II criteria.

4. Why is it clinically dangerous to prescribe an SSRI without first screening for a history of mania or hypomania? Guidance: In a patient with unrecognized bipolar disorder, unopposed antidepressant therapy can precipitate a manic episode or induce rapid cycling, since SSRIs are not protective against mania and lack the mood-stabilizing mechanism needed in bipolar disorder.

Application

5. A 45-year-old reports 3 weeks of insomnia, weight loss, poor concentration, and feeling worthless, but denies ever having a period of elevated mood or decreased sleep need. What is the most likely diagnosis and first-line treatment? Guidance: Major depressive disorder — meets ≥5 SIGECAPS criteria for ≥2 weeks. First-line treatment is an SSRI and/or psychotherapy (CBT/IPT), after screening for suicidality and ruling out medical mimics like hypothyroidism.

6. A patient being treated for depression mentions that last year she went 6 days barely sleeping, talking rapidly, and started three new business ventures, but was still able to work and never needed hospitalization. How does this change her diagnosis and treatment plan? Guidance: This is a hypomanic episode, reclassifying her diagnosis from MDD to Bipolar II Disorder. Treatment shifts from antidepressant monotherapy to mood stabilizers, with antidepressants (if used at all) added cautiously alongside a mood stabilizer.

Analysis

7. Compare how psychotic features would change the clinical picture and urgency in MDD versus Bipolar I mania. Guidance: In severe MDD with psychotic features (e.g., mood-congruent delusions of guilt or worthlessness), this signals a more severe episode requiring closer monitoring and often combination antidepressant-antipsychotic treatment or ECT consideration. In Bipolar I mania, psychotic features (grandiose or paranoid delusions) reflect illness severity and usually require urgent hospitalization and antipsychotic treatment alongside a mood stabilizer, given impaired judgment and safety risk.

8. Why might a clinician relying only on a single-visit snapshot misclassify a bipolar patient as having unipolar MDD, and what history-taking strategy prevents this error? Guidance: Patients most often seek help during depressive episodes and may not spontaneously report past hypomanic/manic periods, especially if those periods felt productive or pleasant rather than distressing. A thorough longitudinal history — directly asking about past periods of elevated mood, decreased sleep need, grandiosity, or impulsive behavior, and ideally corroborated by family/collateral history — is needed to avoid misclassifying bipolar depression as unipolar MDD.

FAQ

Q: What's the practical difference between mania and hypomania? Severity and impairment, not symptom type. Both share the same DIG FAST features, but mania causes marked functional impairment, may include psychosis, and often requires hospitalization; hypomania is noticeable but does not derail the patient's functioning and never includes psychotic features.

Q: Can someone have depression and mania at the same time? Yes — this is called a mixed episode/mixed features specifier, where manic and depressive symptoms occur simultaneously or in rapid alternation. It carries elevated suicide risk because the patient has depressive despair combined with manic energy and impulsivity, a particularly dangerous combination.

Q: Is grief the same as major depressive disorder? No. Grief is a normal, culturally expected response to loss that can include sadness and yearning, typically waxing and waning and connected to thoughts of the deceased. MDD involves persistent, pervasive low mood/anhedonia most of the day nearly every day, meeting full symptom criteria, and can occur alongside or be triggered by grief — but the DSM-5 no longer excludes an MDD diagnosis simply because it follows bereavement.

Q: Why do antidepressants take weeks to work if serotonin levels rise within hours of the first dose? This is one of psychiatry's open questions. While SSRIs increase synaptic serotonin quickly, the clinical antidepressant effect is delayed 2-6 weeks, suggesting the real mechanism involves downstream adaptive changes — receptor sensitivity changes and neuroplasticity/neurogenesis (e.g., BDNF-mediated) — rather than the acute neurotransmitter increase itself.

Q: How do you decide between lithium and valproate for bipolar disorder? Both are first-line mood stabilizers. Lithium has the strongest evidence for reducing suicide risk specifically and is often preferred, but requires monitoring of renal and thyroid function due to a narrow therapeutic index. Valproate is often favored in mixed episodes or rapid cycling and doesn't require the same narrow serum monitoring, but carries teratogenicity risk, making it less favorable in women of childbearing potential.

Quick Revision

• MDD: ≥5 of 9 SIGECAPS symptoms for ≥2 weeks, including depressed mood or anhedonia
• Bipolar I: ≥1 manic episode (≥1 week or hospitalization); depression not required for diagnosis
• Bipolar II: ≥1 hypomanic episode (≥4 days) + ≥1 major depressive episode; no full mania allowed
• Mania vs. hypomania: same DIG FAST symptoms, differ in severity/impairment and possible psychosis (mania only)
• Cyclothymic disorder: subthreshold hypomanic + depressive symptoms for ≥2 years, never symptom-free >2 months
• Persistent depressive disorder (dysthymia): chronic low-grade depression ≥2 years; "double depression" = dysthymia + MDD episode
• Always screen for bipolar history before starting antidepressant monotherapy — risk of manic switch
• Serotonin, norepinephrine, and dopamine dysregulation underlie the monoamine hypothesis of mood disorders
• First-line treatment: SSRIs/SNRIs + psychotherapy for MDD; mood stabilizers (lithium, valproate) ± antipsychotics for bipolar disorder
• Suicide risk is highest during depressive and mixed episodes — always screen for suicidal ideation
• Lithium has the strongest evidence for suicide-risk reduction among mood stabilizers

Related Topics

Prerequisites: Introduction to Psychiatry, DSM-5 diagnostic framework, basic neurobiology of neurotransmitters

Related Topics: Anxiety Disorders, Psychotic Disorders, Clinical Psychopharmacology, Psychiatric Emergencies (suicide risk assessment)

Next Topics: Anxiety Disorders, Schizophrenia and Psychotic Disorders, Clinical Psychopharmacology and Mood Stabilizers