Major Depressive Disorder

Major depressive disorder is the most extensively characterised and clinically significant subtype within the depressive disorder spectrum. It is defined by a discrete episode of at least two weeks duration. The episode combines persistent depressed mood or anhedonia with a defined minimum number of associated cognitive, physical and behavioural symptoms, causing clinically significant distress or functional impairment.

Diagnosis requires exclusion of a substance or medical condition induced mood disturbance. It also requires screening for any history suggestive of previous hypomanic or manic episodes.

Accurately distinguishing this unipolar presentation from bipolar disorder is fundamental, as treatment implications differ substantially.

Diagnostic criteria and classification

• Formal diagnosis requires at least five of the recognised core diagnostic symptoms during the same two week period, representing a change from previous functioning. At least one of the two core symptoms (depressed mood or anhedonia) must be present, with clinically significant distress or functional impairment.
• The symptoms are depressed mood, anhedonia, significant weight or appetite change, sleep disturbance, psychomotor agitation or retardation, fatigue, feelings of worthlessness or excessive guilt, impaired concentration, and recurrent thoughts of death or suicidal ideation.
• Severity is classified as mild, moderate or severe, with severe further subdivided by the presence or absence of psychotic features. Severity guides treatment.
• Severe depression, particularly with psychotic features or significant risk, generally warrants more intensive treatment and closer monitoring than milder presentations, potentially including inpatient psychiatric admission.
• Major depressive disorder with psychotic features is a particularly severe presentation with specific treatment implications. It is characterised by mood congruent delusions (frequently themes of guilt, poverty, nihilism or physical illness) or, less commonly, hallucinations during the depressive episode.

• The symptom pattern and diagnostic criteria are addressed in detail under depressive disorders generally. Major depressive disorder is the discrete, episode based presentation within that category, defined by the minimum symptom count and duration criteria.
• Psychotic features indicate a particularly severe episode, typically with mood congruent delusional content. Themes are consistent with the depressed mood, such as delusions of guilt, poverty or nihilism.
• Nihilistic delusions are delusional beliefs about the non-existence of the self, body or world.
• Psychotic features need specific recognition, given the direct implications for treatment and the generally increased risk in this presentation.
• Suicidal ideation and behaviour, addressed in detail under suicide, require careful, systematic, direct assessment in every patient with major depressive disorder, given the well established, substantial risk in this population.
• Melancholic and atypical features, detailed under depressive disorders generally, may be present. They have some relevance to treatment selection in certain contexts, though the core diagnostic and general management approach remains broadly consistent.

• The essential diagnostic approach is a full clinical psychiatric assessment against the established diagnostic criteria.
• It includes the broader assessment principles detailed under depressive disorders generally: screening for any history of hypomania or mania, screening for an underlying medical cause or contributing medication, and assessment of any coexisting psychiatric condition.
• Specific assessment for psychotic features is essential, given the direct treatment implications. Ask directly about delusional beliefs or hallucinatory experiences during the depressive episode.
• Structured suicide risk assessment, addressed in detail under suicide, is an integral part of every assessment. The identified level of risk informs the approach and the level of ongoing monitoring.

• Management follows the general principles detailed under depressive disorders. Psychological therapy and pharmacotherapy, alone or combined according to severity, are the foundation of treatment for the great majority of presentations.
• Major depressive disorder with psychotic features requires combination treatment with an antidepressant and an antipsychotic, or electroconvulsive therapy, which is generally a particularly effective option for this severe presentation. Antidepressant monotherapy is generally inadequate for this subtype.
• Consider inpatient psychiatric admission in severe major depressive disorder, particularly with significant suicide risk, functional impairment precluding safe community management, psychotic features, or significant physical health compromise (including significant reduction in oral intake).
• The decision is guided by full risk assessment and by whether adequate community based support and monitoring is available as an alternative to admission.
• Electroconvulsive therapy is a particularly effective, rapidly acting option for severe major depressive disorder. It is relevant to psychotic depression, depression with high acute suicide risk, and treatment resistant depression not responding adequately to standard pharmacological and psychological treatment.
• Ongoing, structured, longitudinal management includes maintenance treatment after resolution of the acute episode, given the substantial risk of relapse. After a first episode, maintenance generally extends for a minimum of six to twelve months following symptom resolution. After recurrent episodes it is more prolonged, sometimes indefinite.
• Structured relapse prevention planning and ongoing monitoring underpin long term management, following the broader principles detailed under depressive disorders generally.