Depression is not a monolithic disorder. Rather, it presents in a variety of syndromes that may vary in severity, length, and association of depression with other symptoms. A number of ongoing controversies attend identification and differential diagnosis of depression in late life. This section considers three such issues: common clinical syndromes and diagnoses, major versus minor depressive syndromes, and the question of whether late-life depression is qualitatively different from depressive syndromes at younger ages.
A constellation of mood disorders, many of them involving depression, are identified by DSM-IV. The key symptoms that are used to diagnose various depressive disorders are varied widely. In brief, major depression is characterized by presence of at least five of these symptoms, including one of the defining symptoms (depressed mood, loss of interest/pleasure),at least all or most of the time for 2 weeks or more.
Major depression is most often observed as a single episode or as a series of such episodes; the latter is termed recurrent major depressive disorder. However, major depressive symptoms may also be present in at least two other disorders. First, in bipolar disorder (formerly manic-depressive disorder), depression cycles with periods of excessive optimism, elation, and activity. Bipolar disorder appears to be far less common in older than in younger adults, but it is unclear whether this reflects a true difference in lifetime prevalence across cohorts or simply a change in how the illness manifests in later life. Second, when major depression is accompanied by delusions and/or hallucinations, it is termed psychotic depression.
Older adults with major depressive disorder are far more likely than younger persons to present with psychotic symptoms, particularly delusions. It is nonetheless a relatively rare manifestation, affecting only about 0.1% of elderly community residents.
Even when depressive symptoms are severe, the older individual may not actually be suffering from major depressive disorder. Grief reactions are a good example. Normal bereavement, also referred to as uncomplicated grief, is a response to loss of a loved one or even a valued possession such as one’s home. Symptoms of depression are normal and understandable reactions to such losses, but usually resolve within about 6 months. In a very different vein, depression may also be caused directly by physiological effects of a medical condition unrelated to emotional processes or functions. Such syndromes, termed by DSM-IV as depression due to a general medical condition, are characterized by the same symptoms as, and hence may be difficult to differentiate from, MDD or other depressive disorders. There is some reason to believe that these syndromes are more common among the elderly, if for no other reason than the higher prevalence of many depressogenic diseases in later life.
