Objective: The objective of this study was to compare orthonasal and retronasal olfactory function in PD patients and compare them to NPOD participants and to healthy controls. We hypothesized that the combined testing of orthonasal and retronasal olfactory functions allows to distinguish PD patients from patients with NPOD and healthy controls in regards to their different olfactory impairment patterns.

Background: Olfactory dysfunction (OD) is one of the first clinical signs observed in Parkinson’s disease (PD) and appears several years before the presence of motor disturbance. As a highly reliable symptom OD is present in up to 90% of PD patients. Thus, olfactory testing has the potential to serve as tool for early detection of PD. However, OD is not specific to PD as it affects 20% of the general population. The sense of smell includes an orthonasal and a retronasal component; in some forms of OD, retronasal olfactory function is preserved. We aimed to evaluate whether combined testing of orthonasal and retronasal olfaction allows for discriminating between PD-related OD and non-parkinsonian OD (NPOD).

Method: A total of 32 PD patients, 25 NOPD patients and 15 healthy controls underwent orthonasal (Sniffin’Sticks test) and retronasal (aromatized powders) olfactory testing.

Results: Both orthonasal and retronasal olfaction are impaired in PD and NPOD patients, compared to controls; NPOD patients had significantly better orthonasal scores than PD patients. As a consequence, the ratio of the retronasal score/ orthonasal score was significantly higher in PD than in both other groups. In Parkinson-free participants, orthonasal and retronasal scores were significantly correlated; no such correlation could be observed in PD patients.

Conclusion: For tests of retronasal olfaction, PD patients seem to rely on particular mechanisms to compensate for olfactory loss. Combined orthonasal and retronasal olfactory testing may contribute to differentiate PD patients from patients with NPOD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/retronasal-olfactory-function-in-parkinsons-disease/