Olfactory identification and mild cognitive impairment

Introduction: Mild cognitive impairment (MCI) is a clinical condition between normal ageing and Alzheimer disease (AD). Alzheimer disease is the most frequent reason for dementia; the probability of developing dementia is higher in elderly people with MCI than in the general population in a specified age group.

Aim of the study: To assess whether the smell identification test can be an early marker of MCI and MCI conversion to AD.

Literature on the subject was reviewed and sixteen studies were identified where the smell identification test has been used. Nine of them focused on the comparison of the smell identification test results between MCI patients and the control group. The other seven papers reported on longitudinal studies, where the smell identification test has been evaluated as a marker of conversion from MCI to AD.

Conclusions: The literature review confirms that the smell identification test can be useful in early detection of cognitive impairments, MCI diagnosis and predicting conversion from MCI to AD. Some studies also indicate a relationship between the olfactory dysfunction and deterioration of specific cognitive functions, memory in particular. Early detection of MCI may increase the chances of slowing down the development of dementia. The smell identification test may be used in the diagnosis of MCI in diagnostic batteries together with cognitive functions tests. Longitudinal studies in large groups of elderly people are necessary in order to assess the usability of the smell identification tests and other biomarkers for predicting the occurrence of AD.