Objective: The aim of this study was to investigate the relationship between the degree of olfactory function and motor subtype of Parkinson’s disease (PD).

Background: Parkinson’s disease (PD) is a neurodegenerative disorder with heterogeneous clinical manifestations including various motor and non-motor symptoms (NMS). PD has been classified into subtypes according to the representative motor phenomenology. Olfactory dysfunction in PD is the representative NMS among PD patietns which reflects the anatomical distribution of the underlying pathology and is now widely used as an early clinical sign antecedent to the typical motor signs of PD. As there has been research suggesting that each motor subtype of PD exhibits different anatomical and pathological patterns of degeneration, we sought to determine whether the motor subtypes of PD expressed different degrees of olfactory dysfunction.

Methods: A total of 111 PD patients were recruited. Subjects were divided into tremor dominant type (TDT), akinetic rigid type (ART) and mixed type (MXT) according to classification using part III of the Unified Parkinson’s Disease Rating Scale (UPDRS). An olfactory function test was performed with the Korean version of the Sniffin’ stick (KVSS) test.

Results: Patients with TDT had significantly better olfactory function than patients with ART based on KVSS identification scores (6.5 ± 2.7 in ART, 8.0 ± 2.2 in MXT, 8.6 ± 2.9 in TDT, p =0.002) and TDI scores (17.0 ± 7.0 in ART, 18.7 ± 5.9 in MXT, 22.2 ± 7.5 in TDT, p =0.009). KVSS threshold scores (3.3 ± 2.3 in ART, 4.0 ± 2.2 in MXT, 4.6 ± 2.4 in TDT, p =0.074) and discrimination scores (6.9 ± 4.0 in ART, 6.7 ± 3.1 in MXT, 8.9 ± 3.8 in TDT, p =0.059) were also lower in ART than in TDT, but this difference was not statistically significant.

Conclusions: The results of our study suggested that the degree of olfactory dysfunction differed between PD subtypes. PD patients with TDT had significantly better olfactory function than patients with ART. In summary, olfactory function not only differentiates patients with PD from healthy controls, but also differentiates patients with different motor subtypes of PD. Olfaction, a representative NMS, reflects PD motor phenomenology and may offer further insight into the underlying pathologic distributions of the different subtypes in the central nervous system.

References: Schneider JS, Sendek S, Yang C. Relationship between Motor Symptoms, Cognition, and Demographic Characteristics in Treated Mild/Moderate Parkinson’s Disease. PloS one 2015;10:e0123231.

Iijima M, Kobayakawa T, Saito S, et al. Differences in odor identification among clinical subtypes of Parkinson’s disease. European journal of neurology : the official journal of the European Federation of Neurological Societies 2011;18:425-429

Stern MB, Doty RL, Dotti M, et al. Olfactory function in Parkinson’s disease subtypes. Neurology 1994;44:266-268.

van de Berg WD, Hepp DH, Dijkstra AA, Rozemuller JA, Berendse HW, Foncke E. Patterns of alpha-synuclein pathology in incidental cases and clinical subtypes of Parkinson’s disease. Parkinsonism & related disorders 2012;18 Suppl 1:S28-30.

Siderowf A, Jennings D, Eberly S, et al. Impaired olfaction and other prodromal features in the Parkinson At-Risk Syndrome Study. Movement disorders : official journal of the Movement Disorder Society 2012;27:406-412

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-relationship-between-olfactory-function-and-clinical-subtypes-of-parkinsons-disease/