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- A primary mood disorder characterized by a sustained depressed mood and/or decreased interest in things that used to give pleasure (anhedonia), which represents a change from previous functioning.
- Synonym(s): Unipolar affective disorder, Major depressive disorder
6.6% from 2001 to 2002 in USA (1)
- 16.2% lifetime risk of having major depressive disorder (1)
- Patients can relapse; risk decreases with longer remission period but increases in patients with severe episodes, episodes at a younger age, and multiple episodes.
- Predominant age:
- Low risk before early teens, but highest prevalence in teens and young adults (1)
- Predominant gender
- Females > Males (2:1)
Etiology and Pathophysiology
Complex etiology with 2 major models in the literature (2):
- Monoamine-deficiency hypothesis: Symptoms related to decreased levels of norepinephrine (dullness and lethargy) and serotonin (irritability, hostility, and suicidal ideation) in multiple regions of the brain; other neurotransmitters involved include dopamine, acetylcholine, γ-aminobutyric acid (GABA), glutamate.
- Stress/Hypothalamic-pituitary-adrenal axis: Abnormalities in cortisol response lead to depression; elevated cortisol levels can be associated with depression, but cortisol tests are not indicated for diagnosis.
- Other areas of research interest: Inflammatory processes and abnormal circadian rhythms
- Impaired synthesis/metabolism of neurotransmitters
- Environmental factors and learned behavior may affect neurotransmitters and/or have an independent influence on depression.
Multiple gene loci place a person at increased risk when faced with environmental stressor; twin studies suggest 37% concordance (2).
- Female > Male (2:1)
- Severity of 1st episode
- Persistent sleep disturbances
- Presence of chronic disease(s), recent myocardial infarction (MI), cardiovascular accident (CVA)
- Strong family history (depression, bipolar, suicide, substance abuse), spouse with depression
- Substance abuse and dependence, domestic abuse/violence
- Losses, stressors, unemployment
- Single, divorced, or unhappily married
Commonly Associated Conditions
- Bipolar disorder, cyclothymic disorder, grief reaction, anxiety disorders, somatoform disorders, schizophrenia/schizoaffective disorders
- Medical comorbidity
- Substance abuse