Olfactory dysfunction is associated with motor function only in tremor-dominant Parkinson's disease

Area of Science:

• Neurology
• Neuroscience
• Movement Disorders

Background:

• Olfactory impairment affects 50-90% of Parkinson's disease (PD) patients, representing a common non-motor symptom.
• Previous research explored links between motor, non-motor symptoms, and olfactory dysfunction in PD.

Purpose of the Study:

• To investigate the relationship between olfactory dysfunction (measured by UPSIT) and motor/non-motor symptoms in PD subtypes.
• To analyze these associations separately in tremor-dominant (TD), postural instability and gait difficulty (PIGD), and indeterminate PD subtypes, alongside healthy controls (HCs).

Main Methods:

• Recruited 487 early-stage PD patients and 197 HCs from the Parkinson Progression Markers Initiative (PPMI).
• Collected motor and non-motor data at baseline and after 4 years using standard PD scaling tests.
• Assessed olfactory dysfunction using the UPSIT test.

Main Results:

• Olfactory dysfunction correlated with motor decline specifically in the TD PD subtype.
• Significant associations were found between olfactory dysfunction and processing speed, attention, and executive function in HCs.
• No significant correlations were observed in the PIGD or indeterminate PD subtypes.
• TD patients with anosmia/hyposmia showed worse motor and non-motor scores after 4 years compared to normosmic TD patients.

Conclusions:

• Olfactory dysfunction is significantly associated with motor decline in the TD PD subtype.
• This suggests olfactory dysfunction may act as an early biomarker for motor and non-motor symptoms in the TD subtype of PD.
• The link between olfactory function and disease progression may be less pronounced in other PD subtypes.