Before the dexamethasone suppression test (DST) can be accepted as a
valid diagnostic tool for differentiating depression from dementia, it must
be demonstrated that dementing illnesses per se are not associated with a
positive DST. The authors studied cortisol circadian rhythm and the
overnight DST in 15 nondepressed patients with advanced primary
degenerative dementia and 15 normal control subjects. Seven dementia
patients and no control patients were DST positive. The DST-positive
dementia patients had a blunted predexamethasone circadian cortisol rhythm.
These results cast doubt on the utility of the DST in diagnosing depression
that complicates advanced primary degenerative dementia.