Persistent depressive disorders

**DSM-5 definition (PDD merges chronic MDD and dysthymia):** - Depressed mood for most of the day, more days than not, for ≥2 years in adults (≥1 year in children/adolescents, where mood may be irritable). - Presence of ≥2 of the following while depressed: poor appetite or overeating, insomnia or hypersomnia, low energy/fatigue, low self-esteem, poor concentration/difficulty making decisions, hopelessness. - Never symptom-free for more than 2 consecutive months during the period. - Never met criteria for a manic, hypomanic, or cyclothymic episode. Not better explained by a psychotic disorder, substance, or medical condition. - Symptoms cause clinically significant distress or impairment. - Specifiers: with pure dysthymic syndrome, with persistent major depressive episode, with intermittent major depressive episodes (current or not current episode); early (<21 y) vs late onset (≥21 y); with anxious distress, atypical features, etc. - "Double depression" = superimposed major depressive episode on underlying PDD (a common exam term).

**Epidemiology and risk factors:** - Lifetime prevalence ~3–6%. Women are affected about 2x as often as men. - Risk factors: family history of depression, early life stress or loss, chronic medical illness, and other psychiatric comorbidity (anxiety, substance use, personality disorders). - Onset is often insidious in childhood, adolescence, or early adulthood, and the course is chronic.

**Pathophysiology:** - Similar to MDD: decreased monoamine neurotransmission (serotonin, norepinephrine, dopamine), HPA-axis dysregulation, and genetic and environmental contributions.

**Clinical significance:** - Compared with MDD, symptoms are less severe but more persistent. Patients often describe themselves as "always having been gloomy," and the condition is often underrecognized. - Higher risk of developing MDD (double depression), anxiety disorders, and substance use disorders. Suicide risk is present, especially with a superimposed MDE. - Workup: rule out hypothyroidism (TSH), anemia, substance use, sleep apnea, medication effects, and bipolar disorder.

**Differential diagnosis (high-yield):** - MDD: requires ≥5 symptoms for ≥2 weeks, with episodic rather than chronic course. - Cyclothymic disorder: ≥2 years of hypomanic and depressive symptoms that do not meet full criteria. - Bipolar disorder: any history of mania or hypomania excludes PDD. - Adjustment disorder: onset within 3 months of an identifiable stressor, resolves within 6 months after the stressor ends. - Depressive disorder due to another medical condition or substance/medication-induced depressive disorder.

**Treatment:** - First-line: SSRIs (e.g., sertraline, escitalopram) or SNRIs, psychotherapy (CBT, interpersonal therapy, CBASP — Cognitive Behavioral Analysis System of Psychotherapy), or a combination. Combination therapy is often superior in chronic depression. - Response may be slower, so treatment trials should be adequate (often 8–12 weeks). - Augmentation strategies or switching agents for nonresponse. TCAs and MAOIs are also effective but are second- or third-line because of side effects. - Monitor for emergent suicidality in children and young adults on antidepressants (FDA boxed warning).

**Board pearls:** - Key discriminators on the exam: duration (≥2 years), milder symptoms, and no gap longer than 2 months. - Never manic or hypomanic. Rule this out before starting an antidepressant alone. - Think "PDD" for a vignette with years of low mood, low self-esteem, and poor energy, but intact functioning and no psychosis or suicidality.