Olfactory dysfunctions in neurodegenerative disorders.

Olfactory dysfunction is a common symptom in the patients with neurodegenerative disorders, particularly in Parkinson's disease (PD) and Alzheimer's disease (AD). Recently, studies of olfactory dysfunction have focused on its potential as a medication-independent biomarker for disease progression and as an early indicator for the diagnosis of neurodegenerative disorders. In the past decades, great achievements have been obtained in elucidating the neuroanatomy and the function of olfactory system, yet the pathogenesis of olfactory dysfunction in neurodegenerative disorders remains elusive. The neuropathologic changes of olfactory dysfunction in neurodegenerative diseases may involve the olfactory epithelium, olfactory bulb, primary olfactory cortices, and their secondary targets changes. This article summarizes the up-to-date knowledge on pathophysiological changes of the olfactory system in neurodegenerative disorders and attempts to find the association between olfactory dysfunction and neurodegenerative disorders.