Objective: The objective of this study is to test the hypotheses that: 1) olfactory dysfunction in early stage Parkinson’s disease (PD) is correlated with severity of motor dysfunction, and 2) olfactory dysfunction in early-stage PD is more severe in the nostril contralateral to the motor symptom onset body side compared to the ipsilateral nostril.

Background: PD is a neurodegenerative disease typically with a unilateral motor symptom onset. Olfactory dysfunction is a prevalent non-motor symptom that usually occurs several years before the clinical diagnosis of PD. It is unclear whether smell deficits in the two nostrils are lateralized in early-stage PD and correlate with the severity of the disease.

Method: Smell detection threshold and smell identification test scores of each nostril were collected from 28 cognitively normal Hoehn and Yahr stage-I early-onset idiopathic PD and 27 age-/sex-matched healthy control subjects (Table 1).

Results: Deficits in either smell detection and/or identification function were present in at least one nostril of all PD subjects (Figure 1). Smell identification scores of both early-/later-onset side nostrils were negatively correlated with UPDRS-III side score in both early-/later-onset body sides (r ≤ -0.35, p ≤ 0.03) (Figure 2). There were no significant differences in smell function scores between the sides of nostrils in terms of left/right and early-/later-onset side nostrils relative to the motor symptoms.

Conclusion: This study demonstrated the correlation between smell dysfunction and the severity of motor dysfunction, which suggests that the severity of smell deficits could be used as a marker for disease severity in early stage PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/smell-dysfunction-correlates-with-severity-of-motor-deficits-in-hy-stage-i-early-onset-parkinsons-disease/