Mood disorders

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Mood Disorders: Classification & Clinical Features

Overview

Mood disorders are characterized by a disturbance in the regulation of mood, behavior, and affect. They are subdivided into three broad groups:

Depressive disorders
Bipolar disorders
Depression in association with medical illness or substance/alcohol use

Major depressive disorder (MDD) is differentiated from bipolar disorder by the absence of any manic or hypomanic episode. In the 2019 Global Burden of Disease Study, depression was the single largest factor contributing to disability worldwide, having increased 61% (measured by DALYs) since 1990. In the US alone, lost productivity from mood disorders is estimated at $55.1 billion per year.

Harrison's Principles of Internal Medicine 22E, p. 3709

DSM-5 Classification

I. Depressive Disorders

Disorder	Key Features
Major Depressive Disorder (MDD)	≥1 major depressive episode; no manic/hypomanic history
Persistent Depressive Disorder (Dysthymia)	Chronic depressed mood ≥2 years, less severe than MDD
Disruptive Mood Dysregulation Disorder	Severe recurrent temper outbursts in children
Premenstrual Dysphoric Disorder (PMDD)	Depressive symptoms tied to luteal phase
Substance/Medication-Induced Depressive Disorder	Mood disturbance caused by a substance
Depressive Disorder Due to Another Medical Condition	Direct physiologic consequence of illness

II. Bipolar and Related Disorders

Disorder	Key Features
Bipolar I	≥1 manic episode (may also have depressive episodes)
Bipolar II	≥1 hypomanic + ≥1 major depressive episode; no full mania
Cyclothymic Disorder	Fluctuating hypomanic + depressive symptoms for ≥2 years, not meeting full episode criteria
Other Specified / Unspecified Bipolar	Sub-threshold presentations

Kaplan and Sadock's Synopsis of Psychiatry, p. 1130-1132

Clinical Features of Major Depressive Disorder

Core Symptoms (Mnemonic: SIG E CAPS)

Letter	Symptom
S	Sleep disturbance (early morning awakening / insomnia or hypersomnia)
I	Interest loss (anhedonia)
G	Guilt / worthlessness
E	Energy loss / fatigue
C	Concentration difficulty
A	Appetite change (↓ or ↑) / weight change
P	Psychomotor retardation or agitation
S	Suicidal ideation

Diagnosis requires: ≥5 symptoms for ≥2 weeks, including either depressed mood OR anhedonia; must cause significant impairment.

Neurovegetative Symptoms

~97% of depressed patients report reduced energy
~80% complain of sleep disturbance (especially terminal insomnia - early morning awakening)
Decreased appetite/weight loss is common; reversed neurovegetative symptoms (hypersomnia, hyperphagia) suggest atypical features

Observable Signs

Stooped posture, downward gaze, psychomotor retardation
Decreased rate and volume of speech, delayed responses
In some patients, psychomotor agitation (hand-wringing, hair pulling)
Notably, some patients maintain social composure externally while feeling internally miserable
Kaplan and Sadock's Synopsis of Psychiatry, p. 1168-1170

Severity Specifiers for MDD

Severity	Features
Mild	Minimum symptoms, mild functional impairment
Moderate	Symptoms and impairment between mild and severe
Severe	Many symptoms, marked distress, loss of self-esteem, suicidal ideation, somatic symptoms
Severe with Psychotic Features	As above + hallucinations or delusions (mood-congruent or incongruent)

Important MDD Subtypes / Specifiers

1. Atypical Features

Reversed neurovegetative symptoms: hypersomnia, hyperphagia, weight gain
Mood reactivity (mood brightens to positive events)
Younger age of onset, more severe psychomotor slowing
High comorbidity with anxiety disorders, substance use disorder
May have long-term course or evolve into bipolar I

2. Melancholic Features

Severe anhedonia, early morning awakening, marked psychomotor changes
Worse in the morning, excessive inappropriate guilt

3. Seasonal Pattern (Seasonal Affective Disorder / SAD)

Depressive episodes recur in a particular season, most commonly winter
DSM-5 does not use the term "SAD" but allows the specifier

4. Postpartum Onset

Onset within 4 weeks postpartum
Commonly includes psychotic symptoms

5. Catatonic Features

Stupor, extreme withdrawal, negativism, blunted affect, marked psychomotor retardation
Kaplan and Sadock's Synopsis of Psychiatry, p. 1178-1180

Persistent Depressive Disorder (Dysthymia)

Insidious onset, often before age 25; patients may not seek help for a decade
~20% progress to MDD, ~15% to bipolar II, <5% to bipolar I
Only 10-15% achieve remission at 1 year without treatment
~25% never achieve complete recovery

Bipolar I Disorder - Clinical Features

Defining criterion: At least one manic episode (≥1 week; any duration if hospitalization required)

Manic Episode Symptoms (DSM-5)

Required: Abnormally elevated, expansive, or irritable mood + increased goal-directed activity/energy
Plus ≥3 of the following (or ≥4 if mood is only irritable):
- Grandiosity / inflated self-esteem
- Decreased need for sleep
- Pressured / increased speech
- Flight of ideas / racing thoughts
- Distractibility
- Increased goal-directed activity or psychomotor agitation
- Impulsivity / high-risk behaviors (reckless spending, hypersexuality)

Hypomanic Episode (Bipolar II)

Same symptoms as mania but lasting ≥4 days (not ≥1 week)
NOT severe enough to cause marked impairment or require hospitalization
No psychotic features
Kaplan and Sadock's Synopsis of Psychiatry, p. 1130-1132

Bipolar II Disorder

Defined by at least one hypomanic episode + at least one major depressive episode
No history of full manic episodes
Often misdiagnosed as unipolar MDD (hypomanic episodes are frequently not reported)
Depressive episodes tend to be more frequent and prolonged than in bipolar I

Cyclothymic Disorder

Fluctuating periods of hypomanic and depressive symptoms for ≥2 years (≥1 year in children)
Symptoms never meet criteria for full hypomanic or major depressive episode
Never symptom-free for more than 2 months
Risk of later developing bipolar I or II

Medical / Organic Causes of Depressive Symptoms

A secondary depression workup should rule out:

Category	Examples
Endocrine	Hypothyroidism, Cushing syndrome, Addison disease, diabetes mellitus
Neurologic	Parkinson disease, multiple sclerosis, stroke, epilepsy (temporal lobe), TBI, cerebral tumors
Infectious	Viral hepatitis, HIV/AIDS, infectious mononucleosis, neurosyphilis
Collagen/Autoimmune	SLE, rheumatoid arthritis
Nutritional	Pernicious anemia (B12 deficiency), pellagra
Neoplastic	Pancreatic cancer (40-50% prevalence of depression), disseminated carcinomatosis
Medications	Antihypertensives, glucocorticoids, antiepileptics, opioids, interferon

Kaplan and Sadock's Synopsis of Psychiatry, p. 1187-1189

Prognosis of MDD

First hospitalization for MDD: ~50% recover within 1 year
~25% relapse within the first 6 months post-discharge
30-50% relapse within 2 years; 50-75% within 5 years
Key principle: Each additional episode increases severity and shortens the inter-episode interval

Key Differential Points: MDD vs. Bipolar Depression

Feature	MDD	Bipolar Depression
Manic/hypomanic history	Absent	Present
Family history	More common in bipolar families	Bipolar-specific
Age of onset	Typically later	Typically earlier
Response to antidepressants alone	Generally good	Risk of switching to mania
Atypical features	Less common	More common
Psychomotor slowing	Variable	More pronounced

Sources:

Harrison's Principles of Internal Medicine 22E (2025), Chapter 463, p. 3709-3712
Kaplan and Sadock's Synopsis of Psychiatry, Chapters 6 & 7, p. 1130-1199

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