Parkinson disease in eldery patients: lessons from odour detection thresholds on olfacto-trigeminal interaction

Background: Human nasal chemosensation is mediated by two separate, though interacting sensory pathways: the trigeminal and olfactory systems. Trigeminal sensitivity and olfacto-trigeminal interactions have not yet been well studied in idiopathic Parkinson's disease (IPD). Objectives: The aim of this study was to assess odour detection thresholds in elderly IPD patients, and compare them to the odour detection thresholds of healthy controls. Finally, we investigated potential interactions between trigeminal and olfactory sensitivity. Methods: 89 IPD patients aged over 65 and 89 matched healthy participants were enrolled in the study. Odour detection thresholds to 3 stimuli differentially activating olfactory and trigeminal afferents (Phenyl-ethyl alcohol, n-Butanol and Pyridine) were assessed, using an ascending staircase, binary forced-choice procedure. Results and conclusion: Detection threshold scores were able to discriminate between elderly IPD and controls. Pyridine was less effective than the two other odorants, suggesting that trigeminal pathway is less impaired than the olfactory system. We found that the detection thresholds were significantly different between IPD patients with good autonomy, and patients with impaired autonomy.