Depression assessment and treatment

Major Depressive Disorder, Bipolar Affective Disorder & Mood Stabilisers

Mood disorders represent the leading cause of non-fatal disease burden in Australian clinical medicine. Under guidelines published by the Royal Australian and New Zealand College of Psychiatrists (RANZCP), medical practitioners must master diagnostic phenotyping, pharmacological titration, adverse effect surveillance, and somatic interventions across the depressive and bipolar spectrum.

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Major Depressive Disorder (MDD)

Major Depressive Disorder is a severe, recurring psychiatric illness characterized by persistent disturbances in affect, cognitive processing, vegetative neurobiology, and interpersonal functioning.

Diagnostic Criteria (DSM-5)

A definitive diagnosis of Major Depressive Disorder requires at least 5 of the following 9 symptoms present during the same 2-week period, representing a clear change from prior baseline functioning. Crucially, at least one of the symptoms must be either (1) depressed mood or (2) loss of interest or pleasure (anhedonia).

Clinical Phenotypes and Subtypes

• Melancholic / Biological Depression: Characterized by profound vegetative disturbance: anhedonia that is unreactive to positive events, a distinct quality of depressed mood (felt as physical anguish or emptiness), diurnal variation (regularly worse in the early morning), terminal insomnia (awakening at least 2 hours before normal waking time), marked psychomotor retardation or agitation, significant anorexia, and excessive guilt. Highly responsive to biological therapies (SSRIs, SNRIs, tricyclics, ECT).
• Atypical Depression: Characterized by preserved mood reactivity (mood brightens transiently in response to positive stimuli), leaden paralysis (heavy, lead-like sensation in arms or legs), reversed vegetative signs (hyperphagia with carbohydrate craving, hypersomnia), and long-standing interpersonal rejection sensitivity.
• Psychotic Depression: Depressive episodes complicated by hallucinations or delusions. Psychotic themes are usually mood-congruent (delusions of worthlessness, guilt, financial ruin, severe incurable somatic illness, or Cotard nihilistic delusions). Psychotic depression requires combination therapy with an antidepressant plus an atypical antipsychotic, or urgent Electroconvulsive Therapy (ECT), as antidepressant monotherapy has unacceptably high failure rates.

Assessment and Screening Tools in Australian Practice

• Kessler Psychological Distress Scale (K10): A 10-item questionnaire measuring psychological distress over the past 4 weeks. Heavily embedded in the Australian Medicare system for initiating and reviewing General Practice Mental Health Treatment Plans (MHTP under Better Access).
• Patient Health Questionnaire-9 (PHQ-9): A 9-item scale directly mapping onto the 9 DSM-5 criteria, utilized for grading depression severity (mild: 5–9, moderate: 10–14, moderately severe: 15–19, severe: 20–27) and monitoring longitudinal treatment response.

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Pharmacotherapy of Depression: Assessment and treatment principles

For mild depression, low-intensity psychological strategies (structured physical exercise, sleep hygiene, online CBT such as MoodGYM or MindSpot) are first-line. For moderate to severe MDD, pharmacotherapy combined with evidence-based psychotherapy (Cognitive Behavioural Therapy or Interpersonal Psychotherapy) is the gold standard.

First-Line Antidepressants: SSRIs & SNRIs

• Selective Serotonin Reuptake Inhibitors (SSRIs):
  • First-line choices: Sertraline ($50\text{ to }200\text{ mg}$ daily) and Escitalopram ($10\text{ to }20\text{ mg}$ daily).
  • Antidepressant choice: Sertraline is often suitable in cardiac disease or breastfeeding, but no agent is universally safest for every patient. Review indication, interactions, prior response and perinatal advice.
  • Escitalopram is highly selective but carries a dose-dependent risk of QTc prolongation; maximum dose is capped at $20\text{ mg}$ daily ($10\text{ mg}$ daily in adults aged $\ge 65\text{ years}$).
• Serotonin and Noradrenaline Reuptake Inhibitors (SNRIs):
  • Agents: Venlafaxine ($75\text{ to }225\text{ mg}$ daily) and Duloxetine ($30\text{ to }60\text{ mg}$ daily).
  • Particularly effective in melancholic depression, severe refractory depression, and depression comorbid with chronic neuropathic pain.
  • Noradrenergic activation can cause dose-dependent hypertension; baseline and regular blood pressure monitoring is mandatory.

Key Adverse Effects & Clinical Management

• Gastrointestinal Symptoms: Nausea, loose stools, and dyspepsia occur early due to stimulation of peripheral 5-HT3 receptors; usually self-limiting within 7 to 14 days.
• Sexual Dysfunction: Reduced libido, erectile dysfunction, delayed ejaculation, and anorgasmia occur in up to 30% to 50% of patients and typically persist throughout treatment. Management includes dose reduction, switching to non-serotonergic agents (such as mirtazapine or agomelatine), or adding a PDE-5 inhibitor.
• Hyponatraemia / SIADH: Caused by inappropriate ADH release, particularly in elderly patients, those on concurrent thiazide diuretics, or those with low baseline sodium. Serum electrolytes must be checked at baseline and 2 to 4 weeks after initiation in older adults.
• Bleeding Risk: Platelets take up serotonin from plasma to facilitate aggregation. SSRIs deplete platelet serotonin, doubling the risk of upper gastrointestinal bleeding. Co-prescription with NSAIDs, aspirin, or oral anticoagulants requires gastroprotection with a proton pump inhibitor.
• Black-Box Suicidality Warning: In children, adolescents, and young adults under 25 years of age, initiation of SSRIs/SNRIs can induce a paradoxical transient surge in agitation, akathisia, and suicidal thoughts during the first 1 to 2 weeks before therapeutic mood elevation occurs. Close weekly clinical review is mandatory during early titration.

Therapeutic Trial Duration & Discontinuation

• Adequate Trial: A minimum of 4 to 6 weeks at an established therapeutic dose is required to judge clinical efficacy. If no improvement is observed at 4 weeks, titrate to the maximum tolerated dose or switch to another first-line class.
• Maintenance Duration: Following complete symptomatic remission, antidepressant therapy must continue for at least 6 to 12 months for a first depressive episode to prevent relapse. For recurrent depression ($\ge 2$ or 3 lifetime episodes), maintenance therapy is recommended for at least 2 to 5 years, or indefinitely.
• Stopping antidepressants: Taper collaboratively according to drug, duration, dose and withdrawal symptoms. Some patients need a much slower taper over months. Distinguish withdrawal from relapse and adjust the plan rather than enforcing a universal four-to-eight-week schedule.

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Primary references (checked 7 October 2026): EXTRIP lithium recommendations.