Mood disorders are divided into depressive and bipolar disorders. Worldwide, depressive disorder affects approximately 10% of the population,1 whereas bipolar disorder has a lifetime prevalence of 2.4%.2 In the United States, there is a 21% lifetime prevalence of any mood disorder.3 One urban study showed that 32% of ED patients screened positive for depressive disorder, and 7% screened positive for bipolar disorder.4,5 Depressive disorder affects women twice as often as men, whereas bipolar disorder affects men and women equally. Bipolar disorder is characterized by mania cycling with periods of depression. The depressive periods tend to last longer that the manic periods.
Although mood disorders may occur at any age, the average onset of depressive disorder is about 40 years of age, and that of bipolar disorder is about 30 years of age. There are no differences in prevalence regarding race.6
Depressive disorder is often unrecognized, as the investigation of somatic complaints usually takes priority during patient evaluation.7,8 Adolescents9 and the elderly (especially nursing home patients)10 appear to be particularly vulnerable populations for depression. Increased rates of depressive disorder are seen in many chronic illnesses including CNS diseases,11,12 cardiovascular disorders,13 and cancer.14 Also, patients with depressive disorder have increased risk of certain medical diseases, such as diabetes and coronary artery disease.15
The most common type of depressive disorder is major depressive disorder (also called unipolar or major depression). Diagnosis requires at least 5 of the 10 following symptoms: depressed mood, anhedonia (loss of pleasure in things that used to give pleasure), suicidal ideation with or without a specific plan, significant weight loss or gain, insomnia or hypersomnia, feelings of restlessness, agitation or psychomotor retardation, feelings of worthlessness or inappropriate guilt, fatigue or loss of energy, and difficulty with concentration. At least one of the symptoms must be depressed mood or anhedonia. Symptoms must be present for at least 2 weeks, cannot be due to substance abuse or a medical condition, and must cause significant impairment in normal functioning.16
The pathophysiology of depressive disorder is likely multifactorial including genetic, biological, and psychosocial factors. A genetic predisposition, as evidenced by a 37% concordance rate in twin studies,17 heightens susceptibility. Malfunctioning monoamine neurotransmitters (especially serotonin, norepinephrine, and dopamine)18-20 are implicated and may explain the effectiveness of some current medical therapies. Abnormal γ-aminobutyric acid and glutamate levels in various areas of the brain have been noted.21 Early childhood stress may alter corticotropin-releasing hormone cells in the hypothalamus to heighten future stress responses.22,23 Four areas of the brain involved in normal emotional responses (the prefrontal cortex, anterior cingulate cortex, hippocampus, and amygdala) appear to be altered in patients with depressive disorder. Finally, psychosocial factors including isolation, lack of family support, stressful life events,24,25 and substance abuse ...