Dexamethasone suppression test as a clinical aid in elderly depressed patients

Assessing dementia. Part I: Difficulties, definitions and differential diagnosis

Despite the pressures of an increasingly ageing population and an ever increasing scientific knowledge, the clinical characteristics of dementia remain poorly defined. This relative lack of clarity in clinical understanding has led to diverse diagnostic problems, including those of mistaken diagnosis as well as over- and under-diagnosis in different settings. This paper focuses on the syndromal and aetiological diagnosis of dementia by outlining current clinical definitions, considering differential diagnosis in detail and reviewing characteristics of common dementing disorders. The past emphasis on a search for treatable causes, the reliance on laboratory investigations and the concept of subcortical dementia are all questioned. Aspects of evaluation that are stressed include the value of brief objective cognitive testing, a knowledge of normal age-related cognitive changes, flexible criteria for Alzheimer's disease and a comprehensive individualised evaluation of the person. Broader assessment issues will be dealt with in a second paper.

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.

The dexamethasone suppression test in depressed and non-depressed geriatric medical inpatients

The frequency of an abnormal response to the dexamethasone suppression test (DST) was examined in 38 geriatric patients hospitalized for medical illnesses and affected by depressive disorders diagnosed according to the DSM III, and in 18 medical patients (used as controls) hospitalized in the same ward. Only 11% of the controls and 11% of those affected by dysthymic disorder had an abnormal DST vs 73% of the patients with major depressive disorder (MDD). The sensitivity of the DST for MDD, in this particular setting, was found to be about 73% and the specificity 89%. The importance of this clinical adjunct in diagnosing the severe depressive disorders is discussed.

Dexamethasone suppression test in depression with reversible dementia

Depression with reversible dementia occurs frequently in the elderly and may be a diagnostic problem. The 1-mg dexamethasone suppression test (DST) was performed in 175 elderly psychiatric patients. Abnormal DSTs occurred in both patients with primary degenerative dementia (n = 43, 34.9%) and those with major depression without cognitive dysfunction (n = 59, 66.1%). This finding suggests the presence of common hypothalamic abnormalities in these two disorders. There was no difference in the incidence of abnormal DSTs among depressives with a reversible dementia (n = 28, 78.6%), cognitively intact depressives (n = 59, 66.2%), and depressives who also had primary degenerative dementia (n = 24, 70.8%). An abnormal DST is not clinically useful in predicting the outcome of dementia in depressed patients with cognitive dysfunction.

The dexamethasone suppression test and depressive signs in dementia

The non-suppression by dexamethasone of endogenous cortisol production has been held to be a specific and sensitive indicator of biological depression. Non-suppression has, however, been reported in a proportion of patients with severe dementia. In the present study failure of suppression was found in 10 out of 20 demented patients. The non-suppressors scored significantly higher on a scale of signs of depression. Following antidepressant treatment, 3 out of 8 non-suppressors reverted to normal suppression, but this was not associated with clinical improvements. The implications of these findings are discussed.

The dexamethasone suppression test in patients with presenile and senile dementia of the Alzheimer's type

The dexamethasone suppression test (DST) was performed on 18 patients with presenile and senile dementia of the Alzheimer's type. Objective cognitive testing showed that 13 patients were mildly to moderately impaired and five were moderately to severely impaired. The Hamilton Depression Scale yielded normal results in all patients. The DST results were abnormal in only one of the mildly impaired patients but in four of the five moderately impaired patients. These data suggest that the DST may be a useful clinical tool in mildly impaired patients with Alzheimer's disease but is likely to be confounded by disease in moderately to severely impaired patients.