cyclothymic disorder

DEFINITION / DSM-5-TR CRITERIA - For at least 2 years (1 year in children/adolescents), there are numerous periods with hypomanic symptoms that do not meet full criteria for a hypomanic episode, and numerous periods with depressive symptoms that do not meet full criteria for a major depressive episode. - Symptoms are present at least 50% of the time, and the patient has never been symptom-free for more than 2 consecutive months. - Criteria for major depressive, manic, or hypomanic episodes have never been met. If a full episode occurs, the diagnosis changes (for example, to bipolar I or II). - Not better explained by schizoaffective disorder, schizophrenia, or other psychotic disorders. - Not attributable to substances (for example, stimulants or steroids) or to a medical condition (for example, hyperthyroidism). - Causes clinically significant distress or functional impairment.

EPIDEMIOLOGY AND PATHOPHYSIOLOGY - Lifetime prevalence is about 0.4–1%, with equal rates in men and women. Women are more likely to present for treatment. - Onset is typically in adolescence or early adulthood and the course is insidious and chronic. - There is a genetic overlap with bipolar disorder, and a family history of bipolar disorder is common. The exact pathophysiology is unclear, but it is thought to involve dysregulation of monoaminergic and circadian systems, similar to bipolar disorder. - Roughly 15–50% of patients progress to bipolar I or II disorder.

CLINICAL FEATURES - Mood instability, with alternating mild elevated or irritable mood and mild depressive symptoms. Patients may have decreased need for sleep, increased energy or productivity, impulsivity, and risk-taking during the "up" periods. - The pattern is often mistaken for a personality disorder (borderline) because of unstable relationships and mood reactivity. - Impairment is often in interpersonal and occupational function. - There is a high rate of comorbid substance use and anxiety disorders, plus an increased risk of suicide.

DIFFERENTIAL DIAGNOSIS (boards favorites) - Bipolar II disorder: has at least one full hypomanic episode (≥4 days) and one full major depressive episode (≥2 weeks). - Bipolar I disorder: has at least one full manic episode (≥7 days, or any duration if hospitalization is needed). - Persistent depressive disorder (dysthymia): chronic low mood for ≥2 years with no hypomanic symptoms. - Borderline personality disorder: mood shifts are shorter (hours), tied to interpersonal triggers, and accompanied by identity disturbance, fear of abandonment, and self-harm. - Substance- or medication-induced mood disorder, hyperthyroidism, and ADHD.

MANAGEMENT - Few randomized trials exist, so treatment is extrapolated from bipolar disorder. - Mood stabilizers are first line: lithium, or valproate or lamotrigine as alternatives. - Psychotherapy (CBT, interpersonal and social rhythm therapy, psychoeducation) is important. - Avoid antidepressant monotherapy, which may induce hypomania or mania, rapid cycling, or mood destabilization. - Treat comorbid substance use.

HIGH-YIELD TAKEAWAYS - Think of cyclothymia as a "bipolar-lite" disorder: chronic fluctuations that never reach full criteria. - The duration criterion is 2 years in adults. Compare this with persistent depressive disorder, which also requires 2 years. - The diagnosis requires that no full manic, hypomanic, or major depressive episode has occurred. - Treat with mood stabilizers, not antidepressants alone.