Trigeminal system in Parkinson's disease: A potential avenue to detect Parkinson-specific olfactory dysfunction

Olfactory dysfunction (OD) is very frequent in Parkinson's disease (PD) and observed years before diagnosis. The trigeminal system, a chemosensory system allowing for the perception of spiciness, freshness, etc., is intimately connected to the olfactory system and although usually reduced in OD the trigeminal system is not well characterized in PD. We hypothesize that measuring trigeminal sensitivity potentially allows to discriminate between OD due to PD and OD due to other causes to potentially help the development of an early diagnostic tool.

To evaluate olfactory and trigeminal sensitivity and perception in PD patients and compare them to participants with non-parkinsonian OD (NPOD) and to healthy controls.

We assessed olfactory function using "Sniffin' Sticks test" and trigeminal function with the localization task in 28 PD patients, 27 healthy controls and 21 patients with OD unrelated to PD.

PD patients exhibited significantly higher trigeminal sensitivity than NPOD patients (p = 0.002) and performed similar to healthy controls. In contrast, PD and NPOD patients had both similar olfactory scores, significantly below healthy controls.

The trigeminal system seems not to be impaired in PD patients even in the presence of OD. Measuring trigeminal sensitivity may therefore allow to differentiate PD-related OD from other forms of OD.