Motor Cortex Disinhibition Correlates with Olfactory Dysfunction in Parkinson's Disease

Area of Science:

• Neuroscience
• Movement Disorders
• Olfactory Dysfunction

Background:

• Motor cortex disinhibition, indicated by impaired short-interval intracortical inhibition (SICI) via transcranial magnetic stimulation (TMS), is a known Parkinson's disease (PD) feature.
• The variability of SICI in PD patients is not well understood, raising questions about its origins and clinical significance.

Purpose of the Study:

• Investigate the potential relationship between motor cortex disinhibition and olfactory dysfunction in Parkinson's disease.
• Explore biological links between olfaction and motor function in PD pathogenesis.

Main Methods:

• Assessed motor cortex disinhibition using SICI and olfactory dysfunction via the Sniffin' Stick Test 12 items (SST-12).
• Studied a cohort of early-to-mid-stage PD patients (n=45) and healthy controls (n=35).

Main Results:

• PD patients exhibited decreased cortical inhibition and olfactory function, independent of motor severity.
• Strong evidence showed a correlation between cortical disinhibition and olfactory dysfunction across all participants, patients, and controls.
• Causal inference analysis supported an internal pathogenic mechanism in PD linking these two dysfunctions.

Conclusions:

• Motor cortex disinhibition and olfactory dysfunction may be interconnected by a common, early pathogenic process in Parkinson's disease.
• These findings contribute to understanding PD heterogeneity and potential early diagnostic markers.