Olfaction as a biomarker in Parkinson's disease.

Olfactory dysfunction in Parkinson's disease is common and of interest, both as a clinical finding and potential biomarker. In this article, we discuss studies characterizing the olfactory deficit in Parkinson's disease and pathological analysis that suggests the olfactory system is a likely induction site of the neurodegenerative process. These studies have enabled research to explore the potential of olfactory dysfunction as a key component in early diagnostic strategies, as a biomarker for diagnostic purposes, a predictor of clinical outcomes and a potential therapy-independent marker of disease progression.