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Depression is sometimes referred to as the common cold of mental illness. It is a debilitating disease with significant societal costs. It is, however, one of the most clearly defined and treatable of mental illnesses. Technically, the term "depression" is used to cover a variety of symptomatic conditions, all characterized by negative mood and a loss of pleasure. Together these conditions comprise a spectrum ranging from major depression to dysthymia to adjustment reactions to normal grief and sadness. At one extreme of this continuum lies major depressive disorder, a syndrome characterized by severe episodes of depressed mood accompanied by loss of sleep, appetite, concentration, energy, and hope. The depressed mood must persist for greater than two weeks in order to warrant this diagnosis. At the other end of the continuum lies the diagnosis of dysthymia, which is characterized by a lower level of mood disturbance that persists chronically; that is, involving more days than not for a period of two years or greater. Many patients complain of depressed mood but do not fit neatly into either of these two categories. These patients' symptoms are frequently best accounted for as a reaction to an acute life stressor. These reactions are typically nonpathological and resolve with time, but they may constitute an adjustment reaction if normal functioning is sufficiently disturbed.

Depression is both common and costly. It has a lifetime prevalence of 5 to 10 percent of women and 2 to 5 percent of men. It is an expensive disorder in both direct and indirect terms, as depression causes a higher degree of functional disability than many medical illnesses including diabetes, chronic lung disease, and arthritis. Additional costs to society result from the effect of untreated depression on the treatment of medical illnesses, where it contributes to longer hospital stays and morbidity. This has been particularly well demonstrated in the treatment of myocardial infarction (heart attack), where the presence of major depression has consistently been found to increase mortality.

Depressive illness is thought to result from a combination of biological and psychological factors. The biological component is strongly suggested by the high genetic concordance of depressive disorders. In the twenty-first century, there are various competing theories about the nature of this genetic/biological contribution, but the available data do not yet indicate the specific nature of the illness. The psychological component is similarly suggested by the correlation of onset of major depression with negative life events and with the increased risk of depression in individuals who experienced abuse in childhood. A variety of psychological theories exist and are linked to models of psychotherapeutic treatment. Interpersonal psychotherapists, for example, emphasize the role of grieving due to the loss of an important relationship or a transition in social roles (e.g., transition from working to retirement, marriage to divorce). Cognitive therapists emphasize a mind-set of construing life events in a way that leads to depression. Alternately, psychodynamic therapists search for the ways that unconscious coping processes and repetitive relational patterns result in negative effects. A commonly postulated mechanism would include the turning of anger in on the self. For example, a depressed woman may feel critical of herself rather than direct her anger toward an abusive spouse.

Treatment of depression parallels theories of etiology in that both biological and psychological treatments exist and have been efficacious. A number of different antidepressant medications have been developed, including monoamine oxidase (MAO) inhibitors, tricyclic antidepressants, and selective serotonin reuptake inhibitors (SSRI). These medicines have demonstrated efficacy in both the treatment of acute depressive episodes and in the prevention of relapses. A variety of psychological therapies are also employed in the treatment of depression. Interpersonal psychotherapy and cognitive behavioral psychotherapy are psychotherapeutic models for which depression-specific therapeutic techniques have been developed. These tend to be delivered in the form of brief semi-structured treatments, lasting less than a year in duration. One advantage of these approaches is that they have been well tested in research settings and have an established record of effectiveness in appropriately selected patients. There is also some clinical consensus that long-term psychodynamic (emphasizing unconscious mental processes) therapies are also helpful, especially when the mood disorder exists in the context of a long-standing personality disorder.

JAMES POWERS

STUART J. EISENDRATH

(SEE ALSO: Mental Health)