Study Notes on Major Depressive Disorder (MDD)

Faculty of Health Presentation on Major Depressive Disorder (MDD)

Introduction

  • Presenters: Dr. Bhuvan KC, PhD, FACTM
  • Institution: Queensland University of Technology (QUT)
  • Copyright Note: This material is reproduced under Part VB of the Copyright Act 1968 and is subject to copyright protections.

Welcome to Country

  • Acknowledgement of Traditional Owners:
    • Recognizes Turrbal, Jagera/Yuggera, Kabi Kabi, and Jinibara Peoples as Traditional Owners of the land where QUT is located.
    • Acknowledges the significance of these lands as places of teaching and learning.
    • Pays respect to Elders: past, present, and emerging, and acknowledges Aboriginal and Torres Strait Islander people's role within the QUT community.

Learning Objectives

By the end of the presentation, learners should be able to:

  • Recognize key clinical features of Major Depressive Disorder (MDD).
  • Distinguish between mild and moderate–severe depression.
  • Describe high-level biological models of depression.
  • Outline first-line treatment principles and key safety considerations.

Definition of Major Depressive Disorder (MDD)

  • Key Characteristics:
    • Persistent low mood.
    • Loss of interest or pleasure in activities (anhedonia).
    • Other psychological and somatic symptoms.
  • Diagnostic Criteria:
    • Diagnosis of major depression if at least 5 depressive symptoms are present for a minimum of 2 weeks, with at least one symptom being either a depressed mood or loss of interest in usual activities.
  • Impacts:
    • Causes significant functional impairment in daily life.
    • Cannot be solely attributed to normal grief responses.

Prevalence of MDD in Australia

  • Overall Prevalence: MDD is a high-prevalence condition in Australia.
    • Estimated that 9% of men and 14% of women aged 16–85 have experienced at least one depressive episode during their lives.
    • 12-month prevalence rates: 4% for men and 6% for women.
    • Source: Royal Australian College of General Practitioners (RACGP) Guidelines for Preventive Activities in General Practice.

Pathophysiology of MDD

  • Traditional View: MDD traditionally viewed as a disorder involving monoamine neurotransmission including:
    • Serotonin (5-HT)
    • Noradrenaline (NA)
    • Dopamine (DA)
  • Complexity: MDD is not merely due to a deficiency of neurotransmitters but involves:
    • Dysregulated signaling, receptor function, transporter activity, and downstream pathways.
  • Current Understanding: Recognizes multifactorial neurobiology, factoring in:
    • Monoamines,
    • Glutamate,
    • Neurotrophic factors (e.g., Brain-Derived Neurotrophic Factor - BDNF),
    • Stress hormones (cortisol),
    • Circadian systems (melatonin).

Neurobiological Mechanisms in Depression

Altered Brain Connectivity
  • Key Sites: Dysregulated neural connectivity in mood-regulating circuits:
    • Prefrontal cortex,
    • Limbic system (includes amygdala and hippocampus).
Impaired Neuroplasticity
  • Reduced BDNF signaling and impaired synaptic adaptation.
Stress System Dysregulation
  • Chronic stress leads to elevated cortisol levels, adversely affecting:
    • The hippocampus,
    • The prefrontal cortex.
Circadian Rhythm Disruption
  • Melatonin dysregulation contributes to sleep and mood disturbances.
  • Clinical Relevance: Most antidepressants function by modulating monoamine signaling, with therapeutic effects facilitated by downstream neuroplastic changes.

Core Clinical Features of MDD

  • Common features experienced by individuals include:
    • Low mood.
    • Anhedonia (loss of interest/pleasure).
    • Sleep disturbances.
    • Appetite disturbances.
    • Fatigue or low energy.
    • Poor concentration/indecisiveness.
    • Feelings of worthlessness or excessive guilt.
    • Hopelessness.
    • Suicidal thoughts or behavior (identified as a red flag needing immediate attention).

Risk Factors for MDD

  • Genetic Factors:
    • Family history of depression can increase risk; estimates suggest that approximately 30-40% of depression cases have a genetic component.
    • First-degree family members significantly increase risk (2-3 times higher).
  • Lifetime Experience: 1 in 7 Australians will experience MDD in their lifetime.
  • Gender Differences: Higher lifetime rates of depressive disorders in females, with postpartum depression affecting 10-20% of females.
  • Age Factor: MDD is most prevalent in individuals aged 18-24 years.
  • Chronic Physical Illnesses: Conditions such as coronary heart disease, stroke, diabetes, and cancer correlate with higher rates of depression.
    • References: Byrne EM et al., BMJ Open, 2020; Australian Bureau of Statistics, National Study of Mental Health and Wellbeing, 2020-2022; Mental Health Commission of NSW, National Report Card 2024.

When to Treat MDD

  • Mild Depression:
    • Recommend psychotherapy and lifestyle strategies (indicated by distressing symptoms and some difficulty in usual activities).
  • Moderate–Severe Depression:
    • Antidepressants generally indicated (characterized by several marked symptoms and considerable functional impairment).
  • Severe Depression:
    • Features such as psychosis or suicidal tendencies require specialist care and possibly hospitalization (indicated by marked distress or psychomotor changes leading to minimal functioning).

Non-Pharmacological Management of MDD

  • Psychological Therapies: Such as Cognitive Behavioral Therapy (CBT).
  • Lifestyle Interventions:
    • Emphasis on improving sleep,
    • Regular exercise,
    • Reduction of substance use.
  • Social Support: Importance of community and familial support.
  • Safety Planning: Strategic planning for emergencies such as suicidal thoughts.

Importance of Correct Diagnosis

  • Treatment Safeguarding: Accurate recognition of MDD is crucial to guide safe and effective treatment.
  • Distinctions: MDD must be differentiated from bipolar disorder to avoid misdiagnosis.
  • Urgent Referrals: Red flags necessitate urgent specialist referrals for further assessment.

Conclusion

  • This presentation serves to provide foundational knowledge regarding the understanding, risks, and management of Major Depressive Disorder. Further exploration into treatment modalities will be discussed in Part 2 of the presentation.

Next Steps

  • Follow-Up Content: See Part 2 of MDD for Treatment and Safety considerations.