Psychobiologic features of geriatric affective disorder

Limited work has been done specifically assessing psychobiologic features of depression in the elderly. The biologic characteristics discussed in this article generally discriminate depressed from nondepressed groups in older as well as in younger groups, but they often are not specific for depression and occur in other disorders as well. These markers are not currently useful to make a standard clinical diagnosis in that they lack sufficient sensitivity and specificity. Limitations in this research include the fact that depression is defined phenomenologically, not biologically, and the failure to explicitly study depressive subtypes associated with aging. Other limitations involve the use or reporting of only one biologic characteristic and the lack of knowledge of the pathophysiologic or functional significance of that characteristic. It is likely that some markers identify particular biologic characteristics that may be overrepresented in groups of depressed patients compared with the general population. For example, decreased platelet imipramine-binding density or decreased CSF 5-HIAA may characterize individuals with relative serotonin system deficits who may be at increased risk for depression or suicide or have symptoms related to depression. Or, increased platelet alpha 2-receptor binding or increased EEG alpha may identify individuals who possess noradrenergic or arousal defects associated with depression. The majority of these studies are based on cross-sectional assessments during an acute phase of illness or at death. Longitudinal studies are needed to assess test-retest reliability, state versus trait, and other characteristics. An adequate understanding of the psychobiology of depression in the elderly must address age effects, potential depression subtypes, and age of onset, and finally, it must explain adequately how the biology is related to the depression.