Unipolar disorders

Unipolar disorders are major depressive disorder and dysthymic disorder.

Major Depressive Disorder

Major depressive disorder is diagnosed after a single episode of major depression (Table 2-2). It is characterized by emotional changes, primarily depressed mood, and by so-called vegetative changes, consisting of alterations in sleep, appetite, and energy levels.

Epidemiology

The lifetime prevalence (will occur at some point in a person's life) rate for major depressive disorder is 5% to 20%. The female-male ratio is 2: 1. Race distributions appear equal, and socioeconomic variables do not seem to be a factor. The incidence (rate of new cases) is greatest between the ages of 20 and 40 and decreases after the age of 65.

Etiology

Psychological theories of depression generally view interpersonal losses (actual or perceived) as risk factors for developing depression. In fact, available evidence suggests that childhood loss of a parent or loss of a spouse are associated with depression.

Classic psychoanalytic theories center on ambivalence toward the lost object (person), although more recent theories focus on the critical importance of the object relationship in maintaining psychic equilibrium and self-regard. The cognitive-behavioral model views cognitive distortions as the primary events that foster a negative misperception of the world, which in turn generate negative emotions. The learned helplessness model (based on animal studies) suggests that depression arises when individuals come to believe they have no control over the stresses and pains that beset them.

Biologic, familial, and genetic data support the idea of a biologic diathesis in the genesis of depression. Genetic studies show that depression is found to be concordant more often in monozygotic twins than in dizygotic twins. Unipolar depression in a parent leads to an increased incidence in the offspring of both unipolar and bipolar mood disorders.

Neurotransmitter evidence points to abnormalities in amine neurotransmitters as mediators of depressive states: The evidence is strongest for deficiencies in norepinephrine and serotonin.

Neuroendocrine abnormalities in the hypothalamic-pituitary-adrenal axis are often present In depression and suggest a neuroendocrine link.

Sleep disturbances are near universal complaints in depressed persons. Objective evidence from sleep studies reveals that deep sleep (delta sleep, stages 3 and 4) is decreased in depression and that rapid-eye-movement (REM) sleep alterations include increased time spent in REM and earlier onset of REM in the sleep cycle (decreased latency to REM).

Clinical Manifestations