Objective: To determine if the olfactory deficit in the early-stage Parkinson’s disease (PD) is asymmetric between the two hemispheres ipsilateral and contralateral to the onset body side of PD symptoms in Hoehn & Yahr (H&Y) stage-1 early onset PD patients.

Background: Olfactory dysfunction is prevalent in PD, with deficits in odor detection, identification, and discrimination. The central olfactory system is highly affected by PD pathology. Lewy body deposition, initiates in the olfactory bulb and anterior olfactory nucleus. To date, the cause of olfactory deficits in PD is still not clear. The clinical motor symptoms are always asymmetric at the diagnosis of stage-1 early onset PD. We hypothesize that there is hemispheric asymmetry in olfactory deficits in the patients at this stage.

Methods: The smell identification ability of ten cognitive normal H&Y stage-1 idiopathic PD patients (age 53.8 ± 5.9 years, 4 males, MoCA score 29.4 ± 0.5, 4 subjects with motor symptoms on the right body side) and ten age/sex-matched healthy control subjects (HC) were evaluated using the 40-item University of Pennsylvania Smell Identification Test (UPSIT). Each nostril was tested with 20 items when the other side was air-tight sealed with tape.

Results: There was significant impairment of smell identification function in stage-1 PD compared to the HCs (two-sample t-test, left nostril p = 0.0017; right nostril p = 0.0006). There was no significant difference in UPSIT scores between the left and right nostrils in either PD and HC group (paired t-test, PD p = 0.496; HC p = 0.56). Compared to the nostril ipsilateral to the body side with hemiparkinsonism, the functional deficit in smell identification was significantly worse in the other nostril (paired t-test, p = 0.045).

Conclusions: These preliminary data support the hypothesis of asymmetric functional deficit in olfaction between the hemispheres ipsilateral and contralateral to the onset body side of PD symptoms in stage-1 PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/asymmetric-olfactory-deficit-in-hy-stage-1-early-onset-parkinsons-disease/