Delirium and the dexamethasone suppression test in the elderly

It has been suggested that delirium in the elderly is caused by abnormally high levels of circulating glucocorticoids or by an increased vulnerability to their effects. We performed a dexamethasone suppression test (DST) in 16 consecutive patients without depression or dementia admitted to an acute-care geriatric unit with a clinical diagnosis of lower respiratory tract infection. Seven of 9 (78%) patients who developed delirium were non-suppressors on the DST compared with 1 of 7 (14%) patients without delirium (p = 0.04). Clinical and laboratory indicators of the severity of illness did not differ between the two groups. Of the 8 patients with an abnormal DST, 1 died and another was not available for repeat assessment. On re-examination 8 weeks later, after resolution of the delirium and of the chest infection, 5 of 6 non-suppressors still had an abnormal DST. It is known that some non-demented and non-depressed elderly patients fail to suppress cortisol in response to 1 mg of dexamethasone. Our results suggest that such patients may be at increased risk for developing delirium during acute illness.