DxRxHx
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Clinical Condition Guide

Major
Depressive Disorder

A mood disorder characterized by persistent depressed mood or loss of interest/pleasure, accompanied by cognitive, behavioural, and somatic symptoms that significantly impair functioning.

  • 17%
    Prevalence
  • ~32
    Onset Age
  • 2:1
    Ratio
  • 50-60%
    Response Rate

DSM-5-TR Diagnostic Criteria

  • Core Symptom Requirement

    5+ symptoms during the same 2-week period

    • • At least one must be (1) depressed mood or (2) loss of interest/pleasure

  • Symptom Cluster

    Clinical manifestations:

    • • Depressed Mood (Subjective or observed)
    • • Anhedonia (Markedly diminished interest or pleasure)
    • • Weight/Appetite Change (Significant loss or gain)
    • • Sleep Disturbance (Insomnia or hypersomnia)
    • • Psychomotor Agitation/Retardation (Observable)
    • • Fatigue/Loss of Energy
    • • Worthlessness/Guilt (Excessive or inappropriate)
    • • Concentration Difficulties (or indecisiveness)
    • • Suicidal Ideation (Recurrent thoughts of death)

  • Additional Requirements

    Diagnostic caveats:

    • • Symptoms cause significant distress or impairment
    • • Not attributable to substance use or medical condition
    • • No history of manic or hypomanic episodes

Assessment Protocols

Validated tools for screening and severity tracking

  • PHQ-9

    Patient Health Questionnaire-9

    Brief 9-item self-report measure directly corresponding to DSM-5-TR depression criteria; one of the most widely used screeners in primary care.

    Scoring:

    0-4 minimal, 5-9 mild, 10-14 moderate, 15-19 moderately severe, 20-27 severe depression

    Time:2-5 minutes

  • BDI-II

    Beck Depression Inventory-II

    21-item self-report assessing cognitive, affective, somatic, and vegetative symptoms over past 2 weeks.

    Scoring:

    0-13 minimal, 14-19 mild, 20-28 moderate, 29-63 severe depression

    Time:5-10 minutes

  • MADRS

    Montgomery-Åsberg Depression Rating Scale

    Clinician-rated 10-item scale sensitive to change; preferred for treatment trials and monitoring.

    Scoring:

    0-6 normal, 7-19 mild, 20-34 moderate, >34 severe; change ≥50% indicates response

    Time:15-20 minutes

  • QIDS-SR16

    Quick Inventory of Depressive Symptomatology

    16-item self-report covering all 9 DSM symptom domains; sensitive to change, useful for monitoring.

    Scoring:

    0-5 none, 6-10 mild, 11-15 moderate, 16-20 severe, 21-27 very severe

    Time:5-7 minutes

Causes & Etiology

  • Neurobiological

    • Monoamine dysregulation (serotonin, norepinephrine, dopamine)
    • Reduced hippocampal volume and neurogenesis
    • Prefrontal cortex hypoactivity
    • Amygdala hyperactivity (negative emotional processing)
    • HPA axis dysfunction (cortisol dysregulation)
    • Neuroinflammation and cytokine elevation

  • Genetic

    • Heritability: 30-40% (moderate genetic component)
    • Polygenic risk involving 100+ genes
    • 5-HTTLPR polymorphism (serotonin transporter)
    • BDNF gene variants (neuroplasticity)
    • First-degree relatives have 2-3x increased risk

  • Environmental

    • Early childhood adversity and trauma
    • Chronic stress and major life events
    • Social isolation and lack of support
    • Socioeconomic disadvantage
    • Medical illness (stroke, cancer, chronic pain)
    • Substance use (alcohol, sedatives)

  • Psychological

    • Negative cognitive schemas (Beck's cognitive triad)
    • Rumination and cognitive inflexibility
    • Learned helplessness and external locus of control
    • Perfectionism and self-criticism
    • Reduced reward sensitivity (anhedonia)

Scientific Sources

Evidence-Based

  • PHQ-9 Validation

    Kroenke K, Spitzer RL, Williams JB. The PHQ-9: validity of a brief depression severity measure. J Gen Intern Med. 2001;16(9):606-613.

  • DSM-5-TR Criteria

    American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR). 2022.

  • CBT Efficacy Meta-Analysis

    Cuijpers P, Berking M, et al. A meta-analysis of cognitive-behavioural therapy for adult depression. J Affect Disord. 2013;142(1-3):1-8.

  • Antidepressant Efficacy (STAR*D)

    Rush AJ, Trivedi MH, et al. Acute and longer-term outcomes in depressed outpatients requiring one or several treatment steps: STAR*D trial. Am J Psychiatry. 2006;163(11):1905-1917.

  • Neurobiology of Depression

    Duman RS, Aghajanian GK, et al. Synaptic dysfunction in depression: potential therapeutic targets. Science. 2012;338(6103):68-72.

  • Behavioural Activation

    Dimidjian S, Hollon SD, et al. Randomized trial of behavioural activation, cognitive therapy, and antidepressant medication. J Consult Clin Psychol. 2006;74(4):658-670.

Try it with one patient

Send a PHQ-9 or GAD-7 by secure link and read the scored result before the session.

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