Smell identification test as an indicator for cognitive impairment in Alzheimer's disease

OBJECTIVES: The aim of the present study was to assess olfactory dysfunction in patients with Alzheimer's disease (AD) and to compare utility of the olfactory tests as possible clinical markers. METHODS: Two olfactory identification tests (The Cross-Cultural Smell Identification Test [CC-SIT] and the Picture-based Smell Identification Test [P-SIT]) and the Mini Mental State Examination (MMSE) were administered to patients with AD and age-matched controls. Apolipoprotein E (Apo E) genotypes of patients with AD were identified. RESULTS: Patients with AD had significantly lower olfactory identification scores than age-matched non-demented elderly subjects in both olfactory assessments. In the AD group, the coefficient of correlation between the MMSE scores and the P-SIT scores was higher than that between the MMSE scores and the CC-SIT scores. Receiver operating curve (ROC) analyses for both tests indicated that the P-SIT discriminated AD patients from controls more reliably than did the CC-SIT. Within AD patients, those who were carrying one or two ApoE epsilon4 alleles had a higher coefficient of correlation between the MMSE scores and the P-SIT scores than patients without the ApoE epsilon4 allele. CONCLUSIONS: The results suggest that a short and simple non-lexical olfactory identification test can be useful as a clinical marker of AD appropriate for Japanese elderly population.