The dexamethasone suppression test in geriatric psychiatry

T h e dexamethasone suppress ion test ( D S T ) examines the integrity of the hypothalamopituitary-adrenal (HPA) axis through the suppression by dexamethasone of endogenous cortisol production. Early escape of cortisol production from such suppression by dexamethasone frequently occurs in depressed patients (Carroll, 1982). Promising reports (e.g. McAllister et a/., 1982) of the usefulness of the DST in geriatric psychiatry as an aid to making the clinical distinction between depression and dementia have been overshadowed by a number of studies showing that the test is abnormal as often in dementia as in depressive illness itself. The confounding effects of age on the DST in demented, depressed, and healthy elderly populations have further obscured its diagnostic value in psychogeriatric practice. It is clearly important to review the evidence critically to decide whether the psychogeriatric DST should be consigned to oblivion with some vestige of its former dignity or whether, in appropriate contexts, the test retains any clinical or theoretical value. Many investigators (reviewed by McAllister and Hays, 1987) have studied the dexamethasone suppression test in demented subjects. There have been several reports (e.g. Raskind et al., 1982) that an abnormal DST result (non-suppression) occurs as often in primary degenerative dementia and multi-infarct dementia as in endogenous depression. It is unfortunate that no study in the elderly, and particularly in demented subjects, has measured serum dexamethasone levels. This is crucial both because of possible altered dexamethasone metabolism in old age (Greden et a/., 1986) and because of the likelihood of non-compliance leading to ‘false positive’ apparent non-suppression. In addition, most of these early reports were restricted to severely demented subjects. Since a significant correlation between severity of cognitive deficit and postdexamethasone cortisol was found by Jenike and Albert (1984) and by Pomara el al. (1983), it is possible that in relatively mild dementia, where the differential diagnosis with depression is most difficult, the DST might still be useful. However, no relationship between DST result and severity of cognitive deficit was found by Abou-Saleh et al. (1986) or by Gottfries et a/. (1983). Furthermore, in the only prospective study to date, Alexopoulos et al. (1985) found that there was no significant difference in postdexamethasone cortisol. between depressed sub-jects with cognitive deficits who subsequently recovered, depressed subjects without cognitive deficit, and depressed subjects with coexistent dementia. Carroll’s original (1982) recommendations for a standardized DST procedure assumed, in setting a single cut-off point for postdexamethasone cortisol to identify non-suppressor responses, that demographic factors including age d o not affect the test. Evidence from elderly and younger healthy volunteers is conflicting. Tourigny-Rivard et al. ( 198 1) reported no differences between young and old groups of volunteers, but Georgotas et al. (1986) and Oxenkrug et a/. (1983) reported significant correlations between postdexamethasone cortisol and age. All three groups, however, found very few controls to be non-suppressors. Several studies have reported higher rates of nonsuppression in elderly than in younger depressed patients. Georgotas et al. (1985) found that the effect of age disappeared after correcting for the greater severity of depression in their elderly depressives, but Alexopoulos et a / . (1984) found a higher rate of non-suppression in elderly depressed subjects independent both of severity and clinical subtype of depression. A similar age-related increase in pos tdexamethasone cor t i so l , independent of severity or psychotic features, was reported by Charles et al. ( 1986) and by Davis el a/. (1984). McKeith (1984) found that, within depressed elderly subjects, non-suppression was restricted to those with endogenous symptomatology. Asnis el al. (1981) reported that the correlation between postdexamethasone cortisol