Depression
Depression (major depressive disorder) is a common and serious mood disorder characterised by persistent low mood, loss of interest or pleasure (anhedonia), and a range of associated cognitive, behavioural, and physical symptoms. It is an important differential diagnosis in psychiatry because depressive episodes can present with psychotic features that mimic schizophrenia, and because negative symptoms of schizophrenia can be mistaken for depression.
Why Does This Happen? (First Principles)
💡 FIRST PRINCIPLE: Depression involves dysregulation of monoaminergic neurotransmitter systems (serotonin, noradrenaline, dopamine) in circuits involving the prefrontal cortex, hippocampus, and amygdala. The key distinction from schizophrenia is that the primary disturbance is in mood regulation rather than in thought and perception — when psychotic symptoms occur in depression, they are secondary to and congruent with the low mood.
Clinical Features
Core Symptoms
- Persistent low mood.
- Loss of interest or pleasure (anhedonia).
- Reduced energy and fatigue.
Associated Symptoms
- Sleep disturbance (insomnia or hypersomnia).
- Appetite change with weight loss or gain.
- Psychomotor retardation or agitation.
- Poor concentration and indecisiveness.
- Feelings of worthlessness and guilt.
- Suicidal thoughts or behaviour.
Psychotic Features
In severe depression, psychotic symptoms may occur. These are characteristically mood-congruent — delusions of guilt, worthlessness, nihilism, or deserved punishment.
⚠️ EXAM DETAIL: The distinction between depression and the negative symptoms of schizophrenia is clinically important and can be made using the Calgary Depression Scale for Schizophrenia.
Differential Diagnosis
| Condition | Distinguishing Features |
|---|---|
| schizophrenia | Negative symptoms (alogia, avolition, affective flattening) can mimic depression but lack the subjective experience of low mood. Calgary Depression Scale helps differentiate. |
| schizoaffective-disorder | Both depressive and schizophrenic symptoms present simultaneously at equal intensity. |
| psychotic-depression | Depression with mood-congruent psychotic features; treatment requires antidepressants plus antipsychotics. |
| dementia (pseudodementia) | Cognitive complaints that improve with depression treatment. |
Management
📝 TODO: Needs source — antidepressant classes, psychotherapy (cognitive behavioural therapy [CBT]), electroconvulsive therapy (ECT) for severe/refractory cases.
Exam Focus
Viva Questions
- How do you distinguish depression from the negative symptoms of schizophrenia? (Use the Calgary Depression Scale; depressive symptoms respond to antidepressants, negative symptoms do not.)
- What is pseudodementia? (Depression presenting with cognitive complaints that mimic dementia but improve with treatment.)
MCQ Traps
- ⚠️ EXAM DETAIL: The Calgary Depression Scale for Schizophrenia is specifically designed to distinguish depressive symptoms from negative symptoms and extrapyramidal side effects (EPS) in patients with schizophrenia.
- ⚠️ EXAM DETAIL: Psychotic depression requires combination treatment (antidepressants plus antipsychotics) — antipsychotics alone are insufficient.
Source Notes
- Information in this page is drawn from schizophrenia-vs-depression and the differential diagnosis discussions in schizophrenia, which are sourced from the Handbook of Clinical Psychiatry (de Silva & Hanwella) and the Shorter Oxford Textbook of Psychiatry.