What is unipolar depression?

Unipolar Depression: Definition and Clinical Features

Unipolar depression, also known as major depressive disorder (MDD), is a clinical syndrome lasting at least 2 weeks characterized by depressed mood or anhedonia plus at least 5 of 9 specific symptoms, distinguishing it from bipolar disorder by the absence of manic or hypomanic episodes. 1

Diagnostic Criteria

MDD requires the presence of at least 5 of the following symptoms for at least 2 weeks:

• Depressed mood most of the day, nearly every day
• Markedly diminished interest or pleasure in most activities (anhedonia)
• Significant weight loss/gain or appetite disturbance
• Insomnia or hypersomnia
• Psychomotor agitation or retardation
• Fatigue or energy loss
• Feelings of worthlessness or inappropriate guilt
• Diminished ability to think or concentrate, or indecisiveness
• Recurrent thoughts of death or suicide 1, 2

At least one of the symptoms must be either depressed mood or anhedonia. These symptoms must cause clinically significant distress or impairment in functioning.

Types of Unipolar Depression

Several subtypes of unipolar depression exist:

1. Major Depressive Disorder (MDD) - The primary form with episodes lasting at least 2 weeks
2. Dysthymia - A chronic depressive disorder characterized by depressed mood on most days for at least 2 years 1
3. Subsyndromal Depression (minor depression) - Mood disturbance lasting at least 2 weeks with fewer symptoms than MDD 1
4. Melancholia - A severe form of MDD characterized by loss of pleasure in all activities, lack of reactivity to pleasurable stimuli, early morning awakening, marked psychomotor changes, significant anorexia or weight loss 1

Epidemiology and Impact

Unipolar depression affects approximately 4.4% of the world's population, but rates are significantly higher among cancer patients (14.3%) 1. The condition is associated with:

• Functional impairment
• Poorer physical health outcomes
• Increased risk of suicide
• Lower adherence to medical treatments
• Reduced quality of life
• Increased inflammation and impaired immunity
• Reduced survival rates 1, 3

Assessment Tools

The Patient Health Questionnaire-9 (PHQ-9) is a validated screening tool for depression, with the two-item version (focusing on anhedonia and depressed mood) serving as an initial screen 1:

1. Little interest or pleasure in doing things
2. Feeling down, depressed, or helpless

If a patient scores 2 or 3 on either question, the full PHQ-9 should be completed 1.

Treatment Approaches

Treatment selection depends on depression severity:

Mild Depression

• Psychotherapy alone (CBT or IPT) OR
• SSRI monotherapy 4

Moderate to Severe Depression

• Combination of psychotherapy and medication (SSRIs preferred) 4
• Second-generation antidepressants (SSRIs, SNRIs) are recommended as first-line pharmacological treatment due to better adverse effect profiles and similar efficacy 4

Severe Depression with Suicidal Ideation or Psychotic Features

• Immediate psychiatric consultation
• Possible hospitalization
• Combination treatment with close monitoring 4

Treatment Phases

MDD treatment follows three phases:

1. Acute Phase (6-12 weeks) - Focus on symptom reduction
2. Continuation Phase (4-9 months) - Preventing relapse
3. Maintenance Phase (≥1 year) - Preventing recurrence 4

Prognosis and Long-term Considerations

Unipolar depression should be viewed as a chronic illness rather than a relapsing-remitting disorder 3. Approximately one-third of patients have residual symptoms after treatment, which is associated with:

• Increased risk of short-term relapse
• Long-term chronic course
• Higher suicide attempt risk
• Poor social functioning
• Worse outcomes of comorbid medical conditions 3

Distinguishing from Bipolar Depression

It's crucial to distinguish unipolar from bipolar depression, as treatment approaches differ significantly. Bipolar disorder has a lifetime prevalence of 4% and is characterized by episodes of depression alternating with mania or hypomania 5. Misdiagnosis can lead to inappropriate treatment, as antidepressants may trigger manic episodes in bipolar patients 4.

Monitoring and Follow-up

Regular assessment of treatment response is essential:

• Evaluate within 1-2 weeks of starting treatment
• Monitor for therapeutic response, side effects, and suicidal thoughts
• Continue treatment for at least 4-9 months after achieving remission for first episodes
• Maintain treatment for at least 1 year for recurrent depression 4

Unipolar depression requires vigilant monitoring and often long-term management to prevent recurrence and minimize its substantial impact on morbidity, mortality, and quality of life.