Use of the dexamethasone suppression test with depressed and demented elderly

Although some researchers have suggested that the dexamethasone suppression test (DST) may be useful in differentiating between major depression and dementia in the elderly, recent reports of abnormal DST results in nondepressed, demented elderly have questioned the validity of the test in this population. This study compared the frequency of abnormal DST results in three groups of elderly inpatients: depressed/not demented; demented/not depressed; and depressed and demented. Two geropsychiatrists independently evaluated 33 patients for symptoms of depression and/or dementia and then assigned each patient to one of the three groups. Subjects in the demented/not depressed group had a significantly larger proportion of abnormal DSTs (P less than .01), and the mean postdexamethasone, 4 PM blood cortisol level of the demented/not depressed group was significantly greater than the means of the other two groups (P less than .005). In this sample, the DST was more likely to identify dementia than depression. Until further investigations clarify the parameters of DST use in the elderly, the diagnosis of depression and dementia should continue to be determined by sensitive interpretation of clinical findings, history, and other diagnostic tests.