Objective: Our objective was to investigate the trigeminal pathway by measuring intranasal and central electrophysiological recordings in response to a specific trigeminal stimulus in patients with Parkinson’s disease and compare them to patients with non-parkinsonian forms of olfactory dysfunction and healthy controls.

Background: Olfactory dysfunction is a highly sensitive pre-motor symptom of Parkinson’s disease (PD). In order to use olfactory testing to screen for PD, it is important to differentiate olfactory dysfunction associated with PD from other forms of olfactory dysfunctions. One potential avenue to do so is the measurement of the trigeminal sensitivity. While there is evidence that patients with olfactory dysfunction show a reduced trigeminal sensitivity compared to controls, previous studies suggested that the trigeminal system does not seem to be impaired in PD.

Method: We measured peripheral electrophysiological recordings from the nasal epithelium (negative mucosal potential, NMP) and central EEG-derived event-related-potentials (ERP) in response to a specific trigeminal stimulus (CO2), in 21 PD patients and compare them to 23 patients with non-Parkinsonian olfactory dysfunction (NPOD) and 25 controls (C).

Results: Our results show that patients longer NMP latencies and amplitudes in patients with NPOD than controls and patients with Parkinson’s disease. Moreover, PD patients show larger early ERP components than patients with NPOD. This was despite a significantly diminished olfactory function in both groups of patients compared to controls. These results revealed a discriminant model that could predict group membership for 80% of participants based on the negative-mucosa-potential-latency, olfactory threshold and discrimination tests.

Conclusion: These results suggest a specific pattern of chemosensory impairment in patients with Parkinson’s disease. We are now conducting a study using structural and functional imaging to better understand the underlying mechanisms. This may help to differentiate PD-related olfactory loss from NPOD, a crucial step towards establishing early screening batteries for PD including smell tests.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/specific-chemosensory-pattern-in-parkinsons-disease/