The majority of older adults who suffer from depression experience lower-level symptoms that do not meet diagnostic criteria for major depressive disorder. The DSM recognizes several well-defined disorders that are considered minor depressive states. Dysthymia is defined as presence of one of the two defining symptoms plus at least two other symptoms of depression continuously for a period of at least 2 years. This chronic, low-level depression typically manifests relatively early in life and is in fact less prevalent in older than in younger persons.
However, in a significant number of elderly adults with dysthymic disorder, the syndrome first occurs in middle or late adulthood. This form of dysthymia is less frequently preceded by a major depressive episode and is less likely to be associated with a comorbid personality disorder. In fact, some experts maintain that late-life dysthymia is a disorder qualitatively different from that seen in younger people.
Lower-level depressive syndromes may also be a maladaptive response to emotionally distressing circumstances, as in adjustment disorder with depressed mood. These reactive depressive symptoms may or may not meet diagnostic criteria for major depressive disorder but usually resolve as the individual copes with or adapts to the precipitating event.
These clearly diagnosable disorders cannot account for the majority of non-major depressive syndromes that affect older adults. In fact, the majority of older persons with clinically significant depression may not meet diagnostic criteria for major depressive disorder, dysthymia, or other DSM-defined disorders just reviewed. These individuals nonetheless have significantly compromised quality of life because of their depressed mood.
The prevalence of these less severe forms of depression in elderly has generated a great deal of interest in describing and defining subsyndromal depression among older and younger persons alike. Although some early research suggested that non-major depressive syndromes may be qualitatively different from MDD, the general consensus at present is that they simply represent one point along a continuum of depressive symptomatology. From this perspective, both minor depressive disorders and subsyndromal depressive symptoms are simply a lower-level manifestation of the same basic cognitive, affective, and physiological processes that underlie major depressive disorder, psychotic depression, and other more severe unipolar depressions.
This view of depression as a continuum of symptoms and severity is upheld by a number of lines of evidence. For example, both diagnosable and sub-syndromal minor depressions are clear risk factors for development of major depressive disorder. They have neuroana-tomical characteristics similar to major depressive syndromes and generally respond favorably to the same treatment regimens. Development of a major depressive episode is gradual and may present as a minor or subsyndromal depression in its early stages. Similarly, some apparently lower-level depressive syndromes may represent partial remission or the process of recovery from a more severe depression.
At this point, there is no consensus about how to define subsyndromal depression, and no clear distinction of subsyndromal depression from diagnosable minor depressive illnesses. Nor can researchers or clinicians reliably determine whether subsyndromal symptoms are prodromal to a full-blown major depressive episode. What is agreed upon is the fact that these lower-level depressive symptoms, previously believed to lack the clinical significance to merit diagnosis and treatment, in fact seriously impair quality of life among older adults. Reflecting this realization, the DSM now recognizes subsyndromal depression as a potential diagnosis under the ‘not otherwise specified’ rubric, and there is some impetus to add it as a distinct syndrome when the manual is next revised.
