P2-118: Olfactory testing distinguishes dementia with Lewy bodies (DLB) from Alzheimer’s disease in mild dementia

Abstract

Neuropathologically validated studies have shown that anosmia is more common in patients with DLB and Lewy body variant (LBV) than those with AD. The clinical diagnosis of DLB in life is often missed because consensus criteria lack sensitivity, especially when there is co–existent AD pathology. However, the distinction from AD may be important because those with DLB/LBV are preferential responders to cholinesterase inhibitors. To determine the clinical usefulness of olfactory testing in the differential diagnosis of patients with early dementia. Participants were recruited from the Oxford Project to Investigate Memory and Ageing (OPTIMA) and local clinical services. 47 normal controls, 21 with MCI, 29 with AD (MMSE over 19), and 19 patients with DLB (MMSE over 19) were included after informed consent. Diagnoses of AD, MCI and DLB were based on NINCDS/ADRDA, Petersen and Consensus criteria respectively. Patients with parkinsonism of more than a year duration prior to cognitive impairment, smokers and those with a history or CT suggestive of vascular cognitive impairment were excluded. Olfactory identification was assessed using the validated 16 item ‘sniffin sticks’. Olfactory threshold was assessed using 16 dilutions of n–butanol. The smell identification score was significantly worse for DLB compared to AD (p=0.04). This difference persisted when controlling for age and sex (ANOVA p=0.02) and was independent of cognitive status (MMSE, HVLT and CLOX 1,2). Patients with DLB had the worst impairment on olfactory identification and threshold scores. The mean smell identification scores were DLB 5.05 (SD2.44); AD 6.81 (3.07); MCI 9.0 (3.49) and normal controls 11.81(2.97). The mean smell threshold scores were DLB 1.83 (1.26); AD 2.56 (2.05); MCI 3.51 (2.43) and normal controls 5.47 (2.15). The DLB, MCI and AD groups all had significantly greater impairment in both smell identification and threshold scores compared to normal controls (p<0.01). Simple olfactory tests show significant impairment independent of cognitive status in early DLB compared to early AD and MCI. A bed–side test of smell identification has the potential to improve the identification of DLB cases in mild dementia.