Olfaction and neurodegenerative disease

Abstract

Olfactory dysfunction is an early and common symptom of many neurodegenerative diseases, particularly of Parkinson's disease, Alzheimer's disease, and mild cognitive impairment that heralds progression to dementia. Olfactory impairment is known to be related to several pathologic changes including the deposition of α-synuclein, hyperphosphorylated tau protein, neurofilament protein, Lewy bodies and neuritis inducing a complex cascade of molecular processes such as oxidative stress, neuroinflammation, and cytosolic disruption of cellular processes leading to cell death. The areas mainly showing these pathologic changes are the olfactory epithelium, olfactory bulb and tract, primary olfactory cortices, and their secondary target areas. Since early loss of olfactory function is common among several common neurodegenerative disorders, recent investigations have focused on its utility as a biomarker for early diagnosis and progression. Olfactory impairment appears to be an important sign for early detection, a useful biomarker for disease progression and a useful differentiator between neurological disorders.