Impaired Smell May Help Predict Dementia

Olfactory deficits have been observed in numerous disorders, especially neurodegenerative disorders like Alzheimer’s disease (AD). Several recent studies sought to elucidate this relationship and determine the potential value of odor identification testing for differential diagnosis and early detection of dementia.

In a study reported last year in BMC Neurology, researchers divided participants into two groups: One group consisted of 18 patients with mild cognitive impairment (MCI) and early AD, and the other group consisted of 30 control subjects.1 They tested each participant on measures of olfactory impairment, executive function, and memory, and they measured their brain volumes using 3D magnetic resonance imaging.

The results show that, of the patients who converted to AD during the 6-18 month follow-up period, 71% had scored low on the Brief Smell Identification Test (B-SIT). Only 40% of MCI patients did not convert to AD during that period, and 80% of patients with AD at baseline had reduced scores on the B-SIT. Tests of executive function and memory did not correlate with this change.  

Previous research published in the Archives of Clinical Neurology found similar results using a different type of smell identification test among outpatients with MCI. At a two-year follow-up assessment, 47% of patients with olfactory impairment had progressed to dementia, while only 11% of patients with normal olfaction had converted.2