Neuropsychological correlates of olfactory dysfunction in Parkinson's disease.

Olfactory impairment is a common early non-motor manifestation in Parkinson's disease that has garnered interest as a clinical biomarker for early "pre-motor" diagnosis and prediction of associated clinical phenotypes. Whether olfactory impairment correlates well with motor symptoms is not yet clear, and recent interest has focused on the relationship between hyposmia and other non-motor symptoms. In this paper, we will review emerging evidence for a relationship between hyposmia and neuropsychiatric manifestations, discussing the potential pathophysiology together with challenges and opportunities for future research.