Depression is a state of low mood and aversion to activity. Depressed people may feel sad, anxious, empty, hopeless, helpless, worthless, guilty, irritable or restless. They may lose interest in activities that once were pleasurable, experience loss of appetite or overeating, or problems concentrating, remembering details or making decisions; and may contemplate or attempt suicide. Insomnia, excessive sleeping, fatigue, loss of energy, or aches, pains or digestive problems that are resistant to treatment may be present.
Illnesses featuring depression
A number of psychiatric syndromes feature depressed mood as a main symptom. Mood disorders are a group of disorders considered to be primary disturbances of mood. Within them, major depressive disorder (MDD), commonly called major depression, or clinical depression, is a condition where a person has two or more discrete major depressive episodes. Dysthymia is a condition of chronic depressed mood, the symptoms of which do not meet the severity of a major depressive episode. People suffering bipolar disorder may also experience major depressive episodes.
Outside the mood disorders, chronic dysthymia is also commonly a feature of borderline personality disorder. Adjustment disorder with depressed mood is a mood disturbance appearing as a psychological response to an identifiable event or stressor, in which the resulting emotional or behavioral symptoms are significant but do not meet the criteria for a major depressive episode.
For a discussion of non-psychiatric medical illnesses that cause depression see Depression (differential diagnoses).
Physiology or mechanism
Depression is associated with changes in substances in the brain (neurotransmitters) that help nerve cells communicate, such as serotonin, dopamine and norepinephrine. The levels of these neurotransmitters can be influenced by genetics, hormonal changes, responses to medications, aging, brain injuries, seasonal/light cycle changes, and other medical conditions.
A full patient medical history, physical assessment, and thorough evaluation of symptoms helps determine the cause of the depression. Standardized questionnaires can be helpful such as the Hamilton Rating Scale for Depression, and the Beck Depression Inventory.
A doctor generally performs a medical examination and selected investigations to rule out other causes of symptoms. These include blood tests measuring TSH and thyroxine to exclude hypothyroidism; basic electrolytes and serum calcium to rule out a metabolic disturbance; and a full blood count including ESR to rule out a systemic infection or chronic disease.  Adverse affective reactions to medications or alcohol misuse are often ruled out, as well. Testosterone levels may be evaluated to diagnose hypogonadism, a cause of depression in men.
Subjective cognitive complaints appear in older depressed people, but they can also be indicative of the onset of a dementing disorder, such as Alzheimer's disease. Cognitive testing and brain imaging can help distinguish depression from dementia. A CT scan can exclude brain pathology in those with psychotic, rapid-onset or otherwise unusual symptoms. Investigations are not generally repeated for a subsequent episode unless there is a medical indication.
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Selected cited works
- American Psychiatric Association. Diagnostic and statistical manual of mental disorders, Fourth Edition, Text Revision: DSM-IV-TR. Washington, DC: American Psychiatric Publishing, Inc.; 2000a. ISBN 0890420254.bg:Депресия
- "Depression". National Institute of Mental Health. 2009-09-23. Retrieved 2010-05-22.
- American Psychiatric Association 2000a, p. 355
- Zimmerman M, Chelminski I, Posternak M (2004 Sep). "A review of studies of the Hamilton depression rating scale in healthy controls: implications for the definition of remission in treatment studies of depression". J Nerv Ment Dis. 192 (9): 595–601. PMID 15348975. Check date values in:
- McPherson A, Martin CR (2010 Feb). "A narrative review of the Beck Depression Inventory (BDI) and implications for its use in an alcohol-dependent population". J Psychiatr Ment Health Nurs. 17 (1): 19–30. doi:10.1111/j.1365-2850.2009.01469.x. PMID 20100303. Check date values in:
- Dale J, Sorour E, Milner G. Do psychiatrists perform appropriate physical investigations for their patients? A review of current practices in a general psychiatric inpatient and outpatient setting. Journal of Mental Health. 2008;17(3):293–98. doi:10.1080/09638230701498325.
- Orengo C, Fullerton G, Tan R. Male depression: A review of gender concerns and testosterone therapy. Geriatrics. 2004;59(10):24–30. PMID 15508552.
- Reid LM, Maclullich AM. Subjective memory complaints and cognitive impairment in older people. Dementia and geriatric cognitive disorders. 2006;22(5–6):471–85. doi:10.1159/000096295. PMID 17047326.
- Katz IR. Diagnosis and treatment of depression in patients with Alzheimer's disease and other dementias. The Journal of clinical psychiatry. 1998;59 Suppl 9:38–44. PMID 9720486.
- Wright SL, Persad C. Distinguishing between depression and dementia in older persons: Neuropsychological and neuropathological correlates. Journal of geriatric psychiatry and neurology. 2007;20(4):189–98. doi:10.1177/0891988707308801. PMID 18004006.
- Sadock 2002, p. 108