Smell and preclinical Alzheimer disease: study of 29 patients with amnesic mild cognitive impairment.

OBJECTIVES: To evaluate the olfactory function in patients with amnesic mild cognitive impairment (aMCI) and the relationship to the progression from aMCI to Alzheimer disease (AD).

DESIGN: Cohort prospective study on aMCI patients at the first evaluation (T0) and at the 18-month follow-up (T1).

SETTING: Alzheimer Unit of the University of L'Aquila, Italy.

METHODS: Twenty-nine aMCI patients were enrolled in this study.

MAIN OUTCOME MEASURES: Olfactory function was studied with the Sniffin' Sticks Screening Test (SSST) and the Sniffin' Sticks Extended Test (SSET). Olfactory functions were related to neurocognitive functions assessed by the Mini-Mental State Examination (MMSE) and the Mental Deterioration Battery (MDB).

RESULTS: At T0, aMCI patients showed an olfactory impairment and all of the aMCI patients had lower olfaction scores at T1. At T1, 9 of the 29 aMCI patients (31%) developed AD and had lower mean SSST and SSET scores than 20 aMCI patients who did not develop AD. The most significant relationship was found between olfactory discrimination and visuospatial ability, language skill, and the Rey Immediate test of the MDB and between olfactory identification and the Rey Delayed test.

CONCLUSION: Odour discrimination and identification performance correlated more prominently than detection thresholds with performance on neuropsychological tests. We concluded that the olfactory deficit occurs early in aMCI, so we suggest introducing the clinical routine use of the olfactory test for early identification of the progression of the decline from aMCI to AD.