OLFACTORY DYSFUNCTION AS POTENTIAL BIOMARKER IN NEURODEGENERATIVE DISORDERS

Objectives: olfactory dysfunctions increase with age, 2% of the population under 65 years and 75% over 80 years had olfactory deficits. The main causes of olfactory dysfunctions are viral infections, head trauma and neurodegenerative disorders. Aim of this study is to update current knowledge about the relationship between olfactory dysfunction and neurodegenerative disorders such as Parkinson’s disease (PD)(1), Alzheimer’s disease (AD)(2), progressive supranuclear palsy (PSP), essential tremor (ET) and Huntington’s disease (HD)(3). Methodology: olfactory function is usually evaluated through different approaches, such as psychophysical, electrophysiological and neuroimaging techniques. The main components of olfactory function are odor threshold (OT), identification (OI) and discrimination (OD). Results: According to literature, patients with PD and AD show severe olfactory dysfunction, nevertheless OT is more impaired in PD than in AD, while OI seems more impaired in AD than in PD. OI are normal in ET and PSP, the latter showing also normal OT, both have poor OD. HD show significant deficits only in OI. Interestingly, olfactory dysfunctions often precede motor symptoms of parkinsonism and are investigated as a potential biomarker in subjects at risk (4). Conclusion: olfactory function could help in early detection and differential diagnosis of neurodegenerative disorders.