Olfactory Impairment and Subjective Olfactory Complaints Independently Predict Conversion to Dementia: A Longitudinal, Population-Based Study

Abstract

We examined whether conversion to dementia can be predicted by self-reported olfactory impairment and/or by an inability to identify odors. Common forms of dementia involve an impaired sense of smell, and poor olfactory performance predicts cognitive decline among the elderly. We followed a sample of 1529 participants, who were within a normal range of overall cognitive function at baseline, over a 10-year period during which 159 were classified as having a dementia disorder. Dementia conversion was predicted from demographic variables, Mini-Mental State Examination score, and olfactory assessments. Self-reported olfactory impairment emerged as an independent predictor of dementia. After adjusting for effects of other predictors, individuals who rated their olfactory sensitivity as ''worse than normal'' were more likely to convert to dementia than those who reported normal olfactory sensitivity (odds ratio [OR] 5 2.17; 95% confidence interval [CI] [1.40, 3.37]). Additionally, low scores on an odor identification test also predicted conversion to dementia (OR per 1 point increase 5 0.89; 95% CI [0.81, 0.98]), but these two effects were additive. We suggest that assessing subjective olfactory complaints might supplement other assessments when evaluating the risk of conversion to dementia. Future studies should investigate which combination of olfactory assessments is most useful in predicting dementia conversion. (JINS, 2014, 20, 209-217)

A quantitative meta-analysis of olfactory dysfunction in mild cognitive impairment

“…40 Odour memory may therefore be a salient olfactory domain to monitor over time, as it may differentiate those at risk from those with frank dementia, and changes over time may signal disease progression. Recent evidence indicates that impaired olfaction is associated with the progression from MCI to dementia, 23 which corroborates other longitudinal studies, 194445 but, these studies are limited to odour identification. If AD is signified by the loss of odour identification and odour recognition memory, additional longitudinal studies of odour memory are needed for determining the utility of this deficit as a potential biomarker of transition.…”

Association Between Olfactory Dysfunction and Amnestic Mild Cognitive Impairment and Alzheimer Disease Dementia

“…9-11 Among patients from a memory clinic and volunteer controls, a combination of markers (smell test scores, functional measures, cognitive test scores, imaging measures), more strongly predicted progression from MCI to dementia than age and MMSE. 12 In one prospective study, worse smell scores from a 10-item test predicted conversion from MCI to AD dementia, 3 and in another, the B-SIT performed highly in distinguishing between AD dementia cases and controls.…”

ESPEN guidelines on nutrition in dementia

“…Studies supporting these findings suggest that olfactory impairment is a pre-clinical marker for dementia and that olfactory evaluations may become a supplementary tool in early detection of dementia [27]. APOEe4 carriers seem more prone to suffer from impaired olfactory function before the onset of cognitive impairment [28].…”