Olfactory function and neuropsychological profile to differentiate dementia with Lewy bodies from Alzheimer's disease in patients with mild cognitive impairment: A 5-year follow-up study

• Olfactory and neuropsychological tests were assessed in MCI stage of DLB and AD.
• Smell identification ability was worse in DLB than AD at MCI stage.
• Frontal-executive and visuospatial function were worse in DLB than AD at MCI stage.
• Olfactory and neuropsychological tests can help differentiate DLB from AD at MCI stage.

BackgroundMild cognitive impairment (MCI) is a well-known precursor of Alzheimer's disease (AD) but often also precedes dementia with Lewy bodies (DLB). The early differentiation of DLB from AD is important to delay disease progression. Olfactory dysfunction is a well-known early sign of both AD and Lewy body disorders, including Parkinson's disease (PD) and DLB. Thus, the aim of the present study was to determine whether olfactory and neuropsychological tests can aid in the differentiation of DLB from AD at the MCI stage.MethodsThe present study included 122 MCI patients who were monitored until they developed dementia or until their condition stabilized; the follow-up period averaged 4.9 years (range: 3.9–6.2 years). Baseline olfactory function as measured with the Cross-Cultural Smell Identification (CCSI) test and neuropsychological data were compared.ResultsDuring the follow-up period, 32 subjects developed probable AD (MCI-AD), 18 had probable DLB (MCI-DLB), 45 did not convert to dementia (MCI-stable), and eight developed a non-AD/DLB dementia. The mean CCSI score (95% confidence interval [CI]) in patients with MCI-DLB (4.6; 95% CI: 4.0–5.3) was significantly lower than that of MCI-AD patients (6.4; 95% CI: 6.0–6.7, p < 0.001) and MCI-stable patients (7.3; 95% CI: 6.9–7.8, p < 0.001). The area under the curve of the receiver operating characteristic to discriminate MCI-DLB from MCI-AD using CCSI scores was (0.84; 95% CI: 0.72–0.97). Frontal-executive function and visuospatial ability was worse in patients with MCI-DLB, while verbal recognition memory impairment was greater in those with MCI-AD.ConclusionOlfactory and neuropsychological tests can help predict conversion to DLB or AD in patients with MCI.