Depression for USMLE Step 1 / COMLEX-USA Level 1
Major Depressive Disorder (MDD)
- Pathophysiology:
- Neurotransmitter Imbalance: Implicated neurotransmitters include serotonin, norepinephrine, and dopamine.
- HPA Axis Dysregulation: Increased cortisol levels due to dysregulated hypothalamic-pituitary-adrenal (HPA) axis.
- Neuroplasticity Changes: Reduced hippocampal volume and decreased neurogenesis.
- Clinical Features:
- Persistent sadness, loss of interest in activities (anhedonia), significant weight changes, insomnia or hypersomnia, psychomotor agitation or retardation, fatigue, feelings of worthlessness or excessive guilt, decreased concentration, thoughts of death or suicide.
- Diagnosis:
- Must meet at least five of the symptoms listed above, with at least one of the symptoms being either depressed mood or loss of interest or pleasure, for a minimum duration of two weeks.
Dysthymia (Persistent Depressive Disorder)
- Characteristics:
- Chronic depression lasting at least two years for adults (one year for children and adolescents), with symptoms less severe than those of major depression.
- Symptoms:
- Can include poor appetite or overeating, insomnia or hypersomnia, low energy or fatigue, low self-esteem, poor concentration or difficulty making decisions, feelings of hopelessness.
Adjustment Disorder with Depressed Mood
- Features:
- Emotional and behavioral symptoms in response to an identifiable stressor(s), occurring within three months of the onset of the stressor(s).
- Symptoms:
- Typically include depressed mood, anxiety, and disturbance in conduct that are out of proportion to the severity of the stressor.
Seasonal Affective Disorder (SAD)
- Pathophysiology:
- Related to changes in light exposure; often occurs during the fall and winter months when there is less natural sunlight.
- Treatment:
- Light therapy is the first-line treatment, along with pharmacotherapy and psychotherapy as needed.
Pharmacological Treatments
- Antidepressants:
- Selective Serotonin Reuptake Inhibitors (SSRIs): First-line treatment due to favorable side effect profile.
- Serotonin and Norepinephrine Reuptake Inhibitors (SNRIs): Used for their dual action on serotonin and norepinephrine.
- Tricyclic Antidepressants (TCAs): More side effects, used for treatment-resistant cases.
- Monoamine Oxidase Inhibitors (MAOIs): Least commonly used due to dietary restrictions and potential for severe side effects.
High-Yield Points for USMLE Step 1
- Biological Basis of Depression: Understanding the neurotransmitter systems and brain structures involved.
- Criteria for Diagnosis: Familiarity with the DSM-5 criteria for depression and other mood disorders.
- Mechanisms of Antidepressants: Knowledge of how various classes of antidepressants modulate neurotransmitter systems.
- Side Effects of Medications: Especially the more severe or life-threatening side effects of antidepressants like serotonin syndrome.