Cognitive decline in depressed elderly with olfactory identification impairment.

Olfactory impairment may be a nonspecific early finding in Alzheimer's disease. Many late onset depressives progress to irreversible dementias, but previous research has not identified specific markers for such decline. It was hypothesized that depression and olfactory identification impairment would predict cognitive loss in the elderly. In this study, elderly with and without depression and with and without baseline olfactory identification impairment were compared to evaluate cognitive changes at six-months and relationships between plasma cortisol (CORT) and homocysteine (HC) profiles and cognition. Subjects were 30 community-dwelling elderly (mean age 77 ± six years; 77%F/23%M) recruited by newspaper advertisement. Some had depression and cognitive difficulties, some did not. At baseline and six-month follow-up, subjects completed the Geriatric Depression Scale (GDS), Alzheimer's Disease Assessment Scale (ADAS), Folstein Mini-Mental State Examination (MMSE), Boston Naming Test (BNT), Cain Olfactory Identification Test, plasma levels for basal 8:00 A.M. CORT, post dexamethasone suppression test (DST) CORT, and HC. Subjects were divided into four groups based on median scores on the GDS (above median meaning depressed) and Cain Test (below median meaning impaired olfactory identification ability). Normals (NORMALS) had below median GDS scores and above median Cain scores, Depressed Only (DEP ONLY) had above median GDS scores and above median Cain scores, Olfactory Impaired Only (IMP ONLY) had below median GDS scores and below median Cain scores, and Depressed Olfactory Impaired (DEP/IMP) had above median GDS scores and below median Cain scores. Depressed subjects (DEP ONLY and DEP/IMP) performed significantly worse on baseline MMSE, ADAS and BNT; DEP/IMP subjects were the more cognitively impaired at baseline, and on follow-up showed a trend towards greater cognitive loss. IMP ONLY and DEP/IMP had higher baseline CORT levels and tended towards higher HC; furthermore, the DEP/IMP group showed the greatest baseline cognitive dysfunction and largest six-month loss of cognition. Plasma elevations in CORT and HC seem to be associated with olfactory identification impairment. Whether or not these elevations cause or result in dysfunction of the olfactory system in depressed elderly must be the subject for further research