Anosmia in dementia is associated with Lewy bodies rather than Alzheimer'spathology

Objectives - To assess olfactory function of patients with dementia, Odour detection ability is impaired in clinical Parkinson's disease. Evidence of impaired detection in patients with clinically diagnosed Alzheimer's diseas e is inconsistent. No studies of olfaction have been neuropathologically va lidated. Methods - The olfactory function of 92 patients with dementia and 94 contro ls was assessed using a simple bedside test as part of the Oxford Project T o Investigate Memory and Ageing (OPTIMA). Neuropathological assessment was made of cortical Lewy bodies and substantia nigra (SN) cell counts and of A lzheimer's disease in all 92 patients, 22 of whom had SN Lewy bodies and 43 of whom had only Alzheimer's disease. Results - Patients with Lewy bodies were more likely to be anosmic than tho se with Alzheimer's disease or controls. Patients with Alzheimer's disease were not more likely to be anosmic than controls. Nor was anosmia associate d with degree of neurofibrillary tangles, as assessed by Braak stage. Among subjects with Lewy bodies, overall cortical Lewy body scores and Lewy body density in the cingulate were higher in those who were anosmic, Consensus clinical criteria for dementia with Lewy bodies had a sensitivity of 64% an d specificity of 89%. In the absence of definite Alzheimer's disease, the c riteria had sensitivity of 100%. In patients with definite Alzheimer's dise ase, anosmia was slightly more sensitive (55%) than the consensus criteria (33%). However, the addition of anosmia to the consensus criteria did not i mprove their overall performance. Conclusion - Dementia with Lewy bodies is associated with impaired odour de tection, Misdiagnosis may have accounted for some previous reports of impai red odour detection in Alzheimer's disease. Simple but more sensitive tests of anosmia are required if they are to be clinically useful in identifying patients with dementia with Lewy bodies.