521 - The link between olfactory dysfunction and dementia: the road so far.

Extract

Dementia is characterized by the presence of progressive cognitive impairment losses in the individual’s social and occupational activities. Its etiological diagnosis has therapeutic and prognostic implications. Although its definitive diagnosis depends on neuropathological analysis, detailed anamnesis, physical and neuropsychological tests; biochemical and neuroimaging exams may enable a greater accuracy. Technological innovations using structural and functional neuroimaging methods, as well as biology and molecular genetics techniques, have presented perspectives for the early diagnosis of dementias, particularly Alzheimer’s disease (AD). However, such techniques burden the diagnostic investigation, making its practice unfeasible most the times. The probable link between neurodegenerative diseases and impaired olfactory dysfunction has long been studied. It is suggested that smell tests can be used in dementia’s early detection and differential diagnosis, reducing costs and facilitating the establishment of appropriate treatment. In order to verify the validity of this information, a medical literature search was carried out in may 2021 using PubMed and Cochrane Library, including the terms “olfaction” and “olfactory dysfunction” combined individually with “neurodegenerative disorder”, “dementia” and “Alzheimer’s disease”. Only systematic reviews and meta-analyses written in English from 1991 to 2021 were included. Results show that olfactory impairment in neurodegenerative diseases worsens progressively as patients progress from mild cognitive impairment to AD. It suggests that odor tests could potentially identify AD in the preclinical stages. Although, rigorously designed longitudinal cohort studies are necessary to clarify the value of olfactory identification testing in predicting the onset of AD and its value as an early marker of cognitive decline. In addition, AD patients are more impaired on odor identification and recognition tasks and Parkinson’s Disease (PD) patients on odor detection thresholds tasks, what suggests that PD patients are more impaired on low-level perceptual olfactory tasks whereas AD patients are more strongly impaired on higher-order olfactory tasks involving specific cognitive processes. The results suggest smell tests are a cheaper, simpler to apply and a promising weapon for detecting individuals at risk of dementia.