Olfactory impairment in mild cognitive impairment with Lewy bodies and Alzheimer’s disease

Abstract

Objectives: Impaired olfaction may be a biomarker for early Lewy body disease, but its value in mild cognitive impairment with Lewy bodies (MCI-LB) is unknown. We compared olfaction in MCI-LB with MCI due to Alzheimer’s disease (MCI-AD) and healthy older adults. We hypothesized that olfactory function would be worse in probable MCI-LB than in both MCI-AD and healthy comparison subjects (HC). Design: Cross-sectional study assessing olfaction using Sniffin’ Sticks 16 (SS-16) in MCI-LB, MCI-AD, and HC with longitudinal follow-up. Differences were adjusted for age, and receiver operating characteristic (ROC) curves were used for discriminating MCI-LB from MCI-AD and HC. Setting: Participants were recruited from Memory Services in the North East of England. Participants: Thirty-eight probable MCI-LB, 33 MCI-AD, 19 possible MCI-LB, and 32HC. Measurements: Olfaction was assessed using SS-16 and a questionnaire. Results: Participants with probable MCI-LB had worse olfaction than both MCI-AD (age-adjusted mean difference (B) = 2.05, 95% CI: 0.62–3.49, p = 0.005) and HC (B = 3.96, 95% CI: 2.51–5.40, p < 0.001). The previously identified cutoff score for the SS-16 of ≤ 10 had 84% sensitivity for probable MCI-LB (95% CI: 69–94%), but 30% specificity versus MCI-AD. ROC analysis found a lower cutoff of ≤ 7 was better (63% sensitivity for MCI-LB, with 73% specificity vs MCI-AD and 97% vs HC). Asking about olfactory impairments was not useful in identifying them. Conclusions: MCI-LB had worse olfaction than MCI-AD and normal aging. A lower cutoff score of ≤ 7 is required when using SS-16 in such patients. Olfactory testing may have value in identifying early LB disease in memory services.

Sex differences in brain atrophy in dementia with Lewy bodies

“…DLB females had a thinner olfactory cortex than males. Olfactory alterations can discriminate DLB from AD 40–42 . Nonetheless, previous studies reported no sex differences in odor identification in DLB 40,42 .…”

“…[40][41][42] Nonetheless, previous studies reported no sex differences in odor identification in DLB. 40,42 Investigating sex differences in olfactory identification and their brain correlates could help characterize the less investigated "olfactory bulb only" subtype of DLB. 43 We recently showed that the olfactory cortex is one of the regions that discriminates two DLB subtypes with widespread predominant cortical atrophy and predominant fronto-occipital atrophy.…”

Research diagnostic criteria for mild cognitive impairment with Lewy bodies: A systematic review and meta‐analysis

“…Hyposmia: In one study, self‐reported loss of smell was common in MCI‐LB (44%) and MCI‐AD (19%) 33 . Two studies have measured olfactory function using standardized tests 20, 34 . Both studies found poorer olfactory function in MCI‐LB compared with MCI‐AD, with an AUROC of 0.67 34 and 0.85 20 (Table S2).…”

“…Two studies have measured olfactory function using standardized tests 20, 34 . Both studies found poorer olfactory function in MCI‐LB compared with MCI‐AD, with an AUROC of 0.67 34 and 0.85 20 (Table S2).…”

Properties of odor identification testing in screening for early-stage Alzheimer’s disease

“…Studies involving these factors would help to explore the relationship between olfactory impairment and brain amyloidbeta (Aβ) deposition and neuronal degeneration markers. Also, CSF and PET biomarkers would help in excluding mild cognitive impairment due to dementia with Lewy bodies, which is difficult to differentiate from MCI due to AD with cognitive and olfactory testing alone, according to studies 40 . No participants in the current study had evidence of Parkinsonism, prominent visual hallucinations, or rapid eye movement sleep abnormalities, as required by criteria for probable AD and MCI due to AD by NIA-AA 4,5 .…”