Mood disorders, also termed affective disorders, are characterized by disturbances in emotional state that cause significant distress and functional impairment. These conditions range from unipolar depressive disorders to bipolar spectrum conditions and represent some of the most prevalent and disabling mental health conditions worldwide.
Classification Overview
The DSM-5 classifies mood disorders into two broad categories: depressive disorders and bipolar and related disorders.
| Category | Disorders | Core Feature |
|---|---|---|
| Depressive disorders | Major depressive disorder, persistent depressive disorder (dysthymia), premenstrual dysphoric disorder, disruptive mood dysregulation disorder | Depressed mood and/or loss of interest/pleasure |
| Bipolar disorders | Bipolar I disorder, bipolar II disorder, cyclothymic disorder | Manic/hypomanic episodes plus depressive episodes |
Major Depressive Disorder (MDD)
Major depressive disorder is characterized by one or more major depressive episodes without a history of manic, hypomanic, or mixed episodes. It is one of the most common mental disorders worldwide.
Epidemiology
| Metric | Value |
|---|---|
| Lifetime prevalence | ~15-20% |
| 12-month prevalence | ~7-10% |
| Female:male ratio | 2:1 |
| Mean age of onset | ~30 years |
| Median episode duration | ~4-6 months (untreated) |
| Recurrence rate (after 1 episode) | ~50% |
| Recurrence rate (after 2 episodes) | ~70-80% |
| Recurrence rate (after 3+ episodes) | ~90% |
DSM-5 Diagnostic Criteria
A major depressive episode requires five or more of the following symptoms present during the same two-week period, representing a change from previous functioning. At least one symptom must be either (1) depressed mood or (2) loss of interest or pleasure.
| Criterion | Description |
|---|---|
| 1. Depressed mood | Depressed mood most of the day, nearly every day (subjective report or observation by others) |
| 2. Anhedonia | Markedly diminished interest or pleasure in all, or almost all, activities most of the day, nearly every day |
| 3. Weight/appetite changes | Significant weight loss (not dieting) or weight gain, or decrease/increase in appetite nearly every day |
| 4. Sleep disturbance | Insomnia or hypersomnia nearly every day |
| 5. Psychomotor changes | Psychomotor agitation or retardation nearly every day (observable by others) |
| 6. Fatigue | Fatigue or loss of energy nearly every day |
| 7. Worthlessness/guilt | Feelings of worthlessness or excessive/inappropriate guilt nearly every day |
| 8. Concentration difficulty | Diminished ability to think, concentrate, or indecisiveness nearly every day |
| 9. Suicidal ideation | Recurrent thoughts of death, suicidal ideation, suicide attempt, or specific plan for suicide |
Additional requirements:
- Symptoms cause clinically significant distress or impairment in social, occupational, or other important areas of functioning
- Episode is not attributable to substance use or another medical condition
- Not better explained by a psychotic disorder
Specifiers:
- With anxious distress
- With mixed features
- With melancholic features
- With atypical features (mood reactivity, leaden paralysis, hypersomnia, hyperphagia, rejection sensitivity)
- With psychotic features (mood-congruent or mood-incongruent)
- With catatonia
- With peripartum onset
- With seasonal pattern
Symptom Domains
| Domain | Symptoms |
|---|---|
| Emotional | Sadness, emptiness, hopelessness, anxiety, irritability, apathy |
| Cognitive | Impaired concentration, indecisiveness, memory difficulties, negative thinking, rumination |
| Somatic | Sleep disturbance, appetite changes, low energy, psychomotor changes, pain (headache, backache) |
| Behavioral | Social withdrawal, reduced activity, neglect of responsibilities, substance use |
Pathophysiology
Neurotransmitter systems:
- Monoamine hypothesis: Reduced serotonin, norepinephrine, dopamine activity
- Glutamate and GABA system dysfunction
- Neurotrophic factors: Reduced BDNF (brain-derived neurotrophic factor)
Neuroendocrine:
- HPA axis hyperactivity: Elevated cortisol, CRH dysregulation
- Thyroid axis abnormalities
- Growth hormone alterations
Brain structure and function:
- Hippocampal volume reduction
- Prefrontal cortex hypometabolism
- Amygdala hyperactivity
- Default mode network dysfunction (increased rumination)
Genetic factors:
- Heritability estimate: ~30-40%
- Candidate genes: 5-HTTLPR, BDNF, COMT
- Polygenic risk scores predict susceptibility
Treatment
Pharmacotherapy:
| Class | First-Line | Second-Line | Adjunctive |
|---|---|---|---|
| SSRIs | Fluoxetine, sertraline, escitalopram, paroxetine, citalopram | — | — |
| SNRIs | Venlafaxine, duloxetine, desvenlafaxine | — | — |
| Atypical antidepressants | Bupropion, mirtazapine | — | — |
| TCAs | — | Nortriptyline, amitriptyline, clomipramine | — |
| MAOIs | — | Phenelzine, tranylcypromine | — |
| Other augmentations | — | — | Atypical antipsychotics (aripiprazole, quetiapine), lithium, T3, ketamine |
Psychotherapy:
| Modality | Evidence | Key Elements |
|---|---|---|
| Cognitive-behavioral therapy (CBT) | Strong | Identify/modify negative thinking and behaviors |
| Behavioral activation (BA) | Strong | Increase engagement in rewarding activities |
| Interpersonal psychotherapy (IPT) | Strong | Address interpersonal conflicts and transitions |
| Mindfulness-based cognitive therapy (MBCT) | Strong | Relapse prevention, mindfulness skills |
| Psychodynamic therapy | Moderate | Explore unconscious conflicts and patterns |
Somatic treatments:
- Electroconvulsive therapy (ECT): Highly effective for severe, treatment-resistant, or psychotic depression
- Repetitive transcranial magnetic stimulation (rTMS): FDA-approved for treatment-resistant depression
- Vagus nerve stimulation (VNS): For chronic, treatment-resistant depression
- Ketamine/esketamine: Rapid-acting for treatment-resistant depression and suicidal ideation
Lifestyle interventions:
- Exercise: Comparable to medication for mild-to-moderate depression
- Sleep hygiene
- Nutritional interventions (Mediterranean diet)
- Light therapy (seasonal pattern)
- Social rhythm regulation
Bipolar I Disorder
Bipolar I disorder is characterized by at least one manic episode that lasts at least one week (or requires hospitalization). Depressive episodes are common but not required for diagnosis.
Manic Episode DSM-5 Criteria
A distinct period of abnormally and persistently elevated, expansive, or irritable mood and abnormally and persistently increased goal-directed activity or energy, lasting at least one week and present most of the day, nearly every day (or any duration if hospitalization is necessary).
During the mood disturbance, three or more of the following symptoms are present (four if mood is only irritable):
| Symptom | Description |
|---|---|
| Inflated self-esteem/grandiosity | Unrealistic beliefs about abilities, connections, identity |
| Decreased need for sleep | Feels rested after 3+ hours of sleep than usual |
| Pressured speech | Talks more, talks rapidly, difficult to interrupt |
| Flight of ideas/racing thoughts | Subjective experience of thoughts racing; topic jumping |
| Distractibility | Attention easily diverted by irrelevant stimuli |
| Increased goal-directed activity | Excessive planning, activity; psychomotor agitation |
| Risky behavior | Poor judgment: spending sprees, sexual indiscretion, unwise investments |
Impairment: Marked impairment in social or occupational functioning, or requires hospitalization, or psychotic features.
Bipolar I Disorder Specifiers
| Specifier | Description |
|---|---|
| With anxious distress | Presence of anxiety symptoms during most recent episode |
| With mixed features | Some symptoms of opposite pole present during episode |
| With rapid cycling | Four or more mood episodes in 12 months |
| With psychotic features | Delusions or hallucinations during episode |
| With catatonia | Psychomotor disturbances |
| With peripartum onset | Onset during pregnancy or within 4 weeks postpartum |
| With seasonal pattern | Regular seasonal pattern of episodes |
Epidemiology
| Metric | Value |
|---|---|
| Lifetime prevalence | ~1-2% |
| Female:male ratio (overall) | 1:1 |
| Female:male ratio (rapid cycling) | 3:1 |
| Mean age of onset | ~20 years |
| Manic episode duration (untreated) | ~3-6 months |
| Depressive episode duration (untreated) | ~6-12 months |
| Individuals who also experience psychosis | ~50-70% |
| Lifetime suicide risk | ~15-20 times general population |
Bipolar II Disorder
Bipolar II disorder is characterized by a pattern of hypomanic episodes and major depressive episodes. It requires at least one hypomanic episode and at least one major depressive episode, with no history of manic episodes.
Hypomanic Episode
A hypomanic episode is similar to a manic episode but less severe. The same symptom criteria apply but:
- Duration: At least 4 consecutive days
- No marked impairment in social or occupational functioning
- No psychotic features
- Change in functioning is observable to others
Differences Between Bipolar I and II
| Feature | Bipolar I | Bipolar II |
|---|---|---|
| Manic episodes | Required | Never occurred |
| Hypomanic episodes | May occur | Required |
| Depressive episodes | Common but not required | Required |
| Psychosis during mood episodes | Common (during mania) | Never (by definition) |
| Episode severity | Severe (mania) | Milder (hypomania) |
| Hospitalization | Common during mania | Rare during hypomania |
| Female:male ratio | ~1:1 | ~3:2 (more females) |
Course and Prognosis
Both bipolar I and II are chronic, recurrent conditions:
- Mean number of episodes: 8-10 over lifetime
- Cycle length varies: days to years
- Predominant polarity: Some patients have more depression, others more mania/hypomania
- Inter-episode functioning: Often good, but subsyndromal symptoms common
- Suicide risk: Highest of any psychiatric disorder (standardized mortality ratio ~20-30)
Treatment of Bipolar Disorders
Pharmacotherapy (mood stabilization):
| Medication | Mania | Depression | Maintenance |
|---|---|---|---|
| Lithium | First-line | First-line | First-line |
| Valproate | First-line | Limited | First-line |
| Carbamazepine | First-line | Limited | Second-line |
| Lamotrigine | Not effective for acute mania | First-line (mild-to-moderate) | First-line (depression prevention) |
| Atypical antipsychotics | First-line risperidone, olanzapine, quetiapine, aripiprazole | Quetiapine (monotherapy); olanzapine + SSRI | Olanzapine, aripiprazole, quetiapine |
| Antidepressants | Not used (may induce mania) | Second-line (with mood stabilizer) | Controversial for maintenance |
Key treatment principles:
- Mood stabilizers are the foundation of treatment
- Antidepressants should generally be used with a mood stabilizer to prevent manic switch
- Treat depressive episodes carefully to avoid cycle acceleration
- Psychotherapy (CBT, IPSRT, family-focused therapy) as adjunct
Psychotherapy:
| Modality | Focus |
|---|---|
| Interpersonal and social rhythm therapy (IPSRT) | Stabilize daily routines and sleep-wake cycles |
| Family-focused therapy (FFT) | Improve family communication and problem-solving |
| Cognitive-behavioral therapy (CBT) | Identify early warning signs, manage triggers |
| Psychoeducation | Understanding illness, medication adherence, lifestyle management |
Persistent Depressive Disorder (Dysthymia)
Persistent depressive disorder (formerly dysthymia) is a chronic, low-grade depressive mood that persists for at least two years in adults (one year in children and adolescents).
DSM-5 Criteria
- Depressed mood for most of the day, more days than not, for at least two years
- Presence of two or more of:
- Poor appetite or overeating
- Insomnia or hypersomnia
- Low energy or fatigue
- Low self-esteem
- Poor concentration or difficulty making decisions
- Feelings of hopelessness
- No symptom-free period longer than two months during the two-year period
- No manic/hypomanic episodes
- Not better explained by a psychotic disorder
- Symptoms cause clinically significant distress or impairment
Double Depression
Double depression occurs when a major depressive episode is superimposed on persistent depressive disorder. These individuals have worse outcomes than either condition alone.
| Feature | Dysthymia | MDD | Double Depression |
|---|---|---|---|
| Duration | Chronic (2+ years) | Episodic | Chronic with acute exacerbations |
| Symptom severity | Lower | Higher | Variable (worse during MDE) |
| Functional impairment | Moderate | Severe | Severe |
| Treatment response | Slower, requires longer treatment | Faster | More treatment-resistant |
Treatment
- Pharmacotherapy: SSRIs, SNRIs are first-line; often requires longer treatment course
- Psychotherapy: CBT, PST (problem-solving therapy), psychodynamic therapy
- Combined treatment is more effective than either alone
- Treatment duration: Minimum 6-12 months after remission
Cyclothymic Disorder
Cyclothymic disorder is characterized by chronic, fluctuating mood disturbance with numerous periods of hypomanic symptoms and depressive symptoms that do not meet full criteria for hypomanic or major depressive episodes.
DSM-5 Criteria
- At least two years (one year in children/adolescents) of numerous periods with hypomanic symptoms and depressive symptoms
- During the two-year period, hypomanic and depressive periods are present for at least half the time
- No symptom-free period longer than two months
- Criteria for manic, hypomanic, or major depressive episode have never been met
- Symptoms cause clinically significant distress or impairment
- Not attributable to substance use or another medical condition
Prognosis
| Outcome | Percentage |
|---|---|
| Develop bipolar I or II disorder | 15-50% |
| Continue cyclothymic pattern | Remaining |
| Develop recurrent depressive episodes | 25-50% |
Treatment
- Limited evidence base for pharmacotherapy
- Mood stabilizers (lithium, valproate) often used empirically
- Psychotherapy: CBT, IPSRT
- Lifestyle regulation: Sleep hygiene, routine stabilization, stress reduction
- Avoid antidepressants as monotherapy (risk of cycle acceleration)
Differential Diagnosis of Mood Disorders
| Condition | Key Distinguishing Features |
|---|---|
| Adjustment disorder with depressed mood | Symptoms in response to identifiable stressor, fewer symptoms, <6 months after stressor ends |
| Anxiety disorders | Prominent anxiety/fear without full depressive episode |
| Substance/medication-induced depressive disorder | Onset during or soon after substance intoxication/withdrawal |
| Depressive disorder due to another medical condition | Physical exam, lab findings indicate medical cause |
| Premenstrual dysphoric disorder | Symptoms limited to luteal phase of menstrual cycle |
| Schizoaffective disorder | Psychotic symptoms occur for ≥2 weeks without mood episode |
| ADHD | Early onset, chronic course, core inattention/hyperactivity; no discrete episodes |
| Borderline personality disorder | Chronic instability (mood, relationships, identity); fear of abandonment; no discrete mood episodes |
Special Populations
Peripartum Depression
- Onset during pregnancy or within 4 weeks postpartum
- Affects ~10-15% of women
- Risk factors: History of depression, stressful life events, limited support, hormonal changes
- Treatment: Psychotherapy, SSRIs (consider breastfeeding), support groups
- Untreated maternal depression affects infant attachment and development
Seasonal Affective Disorder (SAD)
- Recurrent major depressive episodes with seasonal pattern (usually fall/winter onset)
- Prevalence increases with latitude
- Symptoms: Hypersomnia, hyperphagia (carbohydrate craving), weight gain, low energy
- Treatment: Light therapy (first-line), CBT-SAD, SSRIs
References
- American Psychiatric Association. (2022). Diagnostic and Statistical Manual of Mental Disorders (5th ed., text rev.). Arlington, VA: APA.
- Belmaker, R. H., & Agam, G. (2008). Major depressive disorder. New England Journal of Medicine, 358(1), 55-68.
- Grande, I., et al. (2016). Bipolar disorder. Lancet, 387(10027), 1561-1572.
- National Institute of Mental Health. (2023). Depression. NIMH.
- National Institute of Mental Health. (2023). Bipolar Disorder. NIMH.
- Kupfer, D. J., et al. (2012). Major depressive disorder: new clinical, neurobiological, and treatment perspectives. Lancet, 379(9820), 1045-1055.
- Geddes, J. R., & Miklowitz, D. J. (2013). Treatment of bipolar disorder. Lancet, 381(9878), 1672-1682.