As our knowledge about depression continues to expand, it is becoming increasingly important to develop a careful and thorough approach to diagnosis. A comprehensive history is necessary to identify various medical causes of depression, any contribution of substance abuse, and a history of psychiatric comorbidities, such as anxiety, psychosis, or personality disorders, because each of these factors can have a major bearing on treatment decisions. It is also no longer sufficient, indeed, if it ever was, to simply diagnose the syndrome of depression. It is now also important to make an effort to understand what subtype of depression the patient may have because this distinction can have a direct bearing on treatment decisions. Finally, it is always necessary to conduct a careful assessment of the risk of suicide, including ongoing monitoring of suicide risk, given the inherent risk of suicide that depression can pose.

Criteria The use of psychiatric epidemiologic data led to the establishment of diagnostic criteria for depression. These criteria continue to be refined and are published in the Diagnostic and Statistical Manual of Mental Disorders of the American Psychiatric Association (CDSM-IV). The current diagnostic criteria for depressive illnesses. Despite the use of these criteria, the determination of the "clinical significance" of behavioral or psychological syndromes causing either "distress" or "disability" is more art than science. Distinguishing between significant psychopathology and normal variants is no easy task, even for experienced clinicians.

The presence of depressed mood is one of the two core criteria for the diagnosis of depression. Depressed mood, however, can mean different things to different people and may be described as anguish, anxiety, irritability, or mournfulness. In addition, depression may have a somatic presentation. Common somatic expressions of depression include headache, epigastric pain, and chest discomfort. Depression manifesting as somatic symptoms is more commonly seen in the elderly and in people who have difficulty describing feelings and physical sensations. Somatoform manifestations of depression appear to disproportionately affect women.

Loss of interest, or anhedonia, is a symptom that it is also critical to explore; it is the other core criterion for the diagnosis of depression. The easiest way to demonstrate anhedonia is to identify the loss of previously pleasurable pastimes. This loss can be so severe that the patient exhibits no enjoyment of friends, family, or career.

Screening for Depression

Using a screening instrument for depression in primary care settings can provide a ready way to identify whether depressive symptoms are present and, consequently, require further attention. A number of instruments have been used over the years, including the Beck, Carroll, Center for Epidemiologic Studies, and Zung scales. These scales are straightforward to use and can be scored by office staff within minutes. The Hamilton Depression Scale is the one most frequently used in research settings and by psychiatrists, but its use requires some training and an interview required. The Carroll Scale has the advantage most closely resembling the Hamilton Depression Scale, but can be self-administered. A scoring system has been developed for the Carroll Scale, with 0 to 11 points indicating no or minimal depression, 12 to 18 points indicating mild depression, 19 to 25 points indicating moderate depression, and 26 or more points indicating severe depression. However, there is no clear cutoff point for where depression does or does not exist, and the clinician is still left with deciding when further inquiry into the nature of symptoms identified on these scales is necessary.