Can you tell me about the diagnosis and treatment of major depressive disorder (MDD)?

Diagnosis and Treatment of Major Depressive Disorder

Diagnosis

Diagnose MDD using validated diagnostic instruments (SCID or MINI) combined with clinical assessment scales (MADRS-10 or QIDS-SR) to confirm a major depressive episode characterized by depressed mood or anhedonia plus additional symptoms lasting at least 2 weeks with functional impairment 1.

Essential Diagnostic Steps:

• Screen with PHQ-9: Start with the 2-item version (anhedonia and depressed mood). If score ≥2, complete all 9 items 2
• Severity stratification by PHQ-9 score:
  • Mild: 1-7
  • Moderate: 8-14
  • Moderately severe: 15-19
  • Severe: 20-27

Critical Exclusions Before Diagnosing MDD:

• Bipolar disorder (use SCID or MINI)
• Active severe substance use disorder
• Personality disorders mimicking depression
• Medical conditions causing depressive symptoms 3, 1

Risk Factors to Document:

• Prior mood disorder episodes
• Comorbid anxiety disorders
• Chronic medical illnesses
• Recurrent/advanced disease states
• Social isolation (single, widowed, divorced)
• Unemployment and financial strain
• Lower educational attainment 2

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Initial Treatment Selection

For moderate to severe MDD, initiate monotherapy with either cognitive behavioral therapy (CBT) OR a second-generation antidepressant (SGA) based on patient preference, cost, accessibility, and adverse effect tolerance 1, 4.

Treatment Algorithm by Severity:

Mild MDD (PHQ-9: 1-7):

• Start with CBT monotherapy 4
• Reserve SGAs for patients who prefer medication or lack CBT access

Moderate to Severe MDD (PHQ-9: ≥8):

• First-line options (choose ONE):
  • CBT monotherapy
  • SGA monotherapy
  • Combination CBT + SGA (if rapid response needed or severe symptoms) 4

Selecting Among Second-Generation Antidepressants:

All SGAs have comparable efficacy—select based on adverse effect profile, cost, and patient-specific factors 5, 1:

• SSRIs (sertraline, escitalopram, citalopram, fluoxetine, paroxetine): First consideration for most patients
• SNRIs (venlafaxine, duloxetine): Consider if comorbid pain or neuropathy
• Others (bupropion, mirtazapine, trazodone):
  • Bupropion: If sexual dysfunction concerns or need smoking cessation
  • Mirtazapine: If insomnia or appetite loss prominent
  • Trazodone: Primarily for insomnia augmentation 6

Dosing Requirements:

• Start at minimum licensed dose
• Titrate to therapeutic range within 1-2 weeks
• Maintain for minimum 4 weeks before assessing response 3, 5

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Monitoring and Assessment

Evaluate treatment response within 1-2 weeks of initiation, then regularly using measurement-based care with PHQ-9 or MADRS-10 5, 6.

Response Definitions:

• Response: ≥50% reduction in symptom severity
• Remission: PHQ-9 <5 or MADRS-10 <10
• Partial response: 25-49% improvement
• Non-response: <25% improvement 3

Timeline for Treatment Decisions:

• Week 1-2: Assess tolerability and early response
• Week 4-6: Determine adequate response vs. need for modification
• Week 6-8: If inadequate response, implement second-step strategy 5, 6

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Second-Step Treatment for Inadequate Response

For patients with <50% improvement after 6-8 weeks of adequate-dose SGA monotherapy, either switch to a different mechanism SGA OR augment with CBT or a second pharmacologic agent 4.

Switching Strategies:

Switch to different mechanism of action (use Neuroscience-based Nomenclature to confirm different mechanism) 3:

• From SSRI → SNRI, bupropion, or mirtazapine
• From SNRI → SSRI, bupropion, or mirtazapine
• Taper first agent while initiating second (avoid abrupt discontinuation)

Augmentation Strategies:

Pharmacologic augmentation options 6:

• Second-generation antipsychotics (aripiprazole, quetiapine, brexpiprazole): Evidence-based for augmentation
• Bupropion: Add to SSRI/SNRI
• Mirtazapine: Add to SSRI/SNRI
• Lithium: For severe or recurrent depression

Non-pharmacologic augmentation:

• Add CBT to ongoing SGA therapy 4

Advanced Interventions for Treatment-Resistant Depression:

Define TRD as failure of ≥2 adequate trials (minimum licensed dose for ≥4 weeks each) of SGAs with different mechanisms of action, with <25% improvement to both 3.

For TRD, consider:

• Repetitive transcranial magnetic stimulation (rTMS) 6
• Ketamine or esketamine (for severe, acute suicidality or TRD) 6
• Electroconvulsive therapy (ECT): Most effective for severe TRD 6

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Continuation and Maintenance Treatment

Continue treatment for 4-9 months after achieving remission for first episode; consider longer duration (≥1 year) for patients with ≥2 prior episodes 5, 1.

Relapse Prevention:

• Maintain same dose that achieved remission
• Continue measurement-based monitoring (monthly PHQ-9)
• Address residual symptoms aggressively
• Consider indefinite maintenance for ≥3 episodes or severe recurrent depression 5

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Common Pitfalls to Avoid:

1. Inadequate dosing: Ensure minimum licensed dose maintained for full 4-6 weeks before declaring failure
2. Premature switching: Allow adequate trial duration (6-8 weeks) unless intolerable adverse effects
3. Ignoring adherence: Assess medication adherence before escalating treatment
4. Missing bipolar disorder: Always screen for manic/hypomanic episodes before initiating antidepressants
5. Monotherapy bias: Combination therapy (CBT + SGA) is evidence-based for moderate-severe MDD, not just monotherapy 4
6. Neglecting psychotherapy: CBT has equivalent efficacy to SGAs and should be offered as first-line option 1, 4