How the Side of Onset in Parkinson's Disease Influences Its Progression

Parkinson's disease affects approximately 10 million individuals worldwide and is characterized primarily by motor symptoms such as tremors, muscle rigidity, and slowed movement. Interestingly, the disease often initially impacts only one side of the body, a phenomenon called asymmetrical onset, which has significant implications for the disease’s progression.

Recent research by the University of Geneva and Geneva University Hospitals has shed light on how the side of the first symptom presentation can influence not only motor disturbances but also the cognitive, emotional, and psychiatric aspects of Parkinson’s disease. Their groundbreaking study, published in npj Parkinson’s Disease, reveals that patients exhibiting symptoms on the right side of their body—indicative of dysfunction in the brain’s left hemisphere—are more susceptible to widespread cognitive decline and a greater risk of developing dementia. Conversely, those with initial symptoms on the left side—linked to right hemisphere dysfunction—are at higher risk of psychiatric issues such as depression and anxiety, as well as difficulties in emotional recognition.

This discovery underscores the importance of personalized treatment strategies that consider the side of symptom onset. Historically, Parkinson's research has focused heavily on motor symptoms, often neglecting non-motor components, which can significantly affect a patient’s quality of life.

Dr. Julie Péron, who led this research, emphasizes that these findings mark a crucial advance in understanding the non-motor manifestations of Parkinson's, suggesting that evaluating the asymmetry of symptoms should become a routine part of diagnosis. Accurate assessment of motor asymmetry could facilitate early intervention and enable tailored therapies that address both motor and non-motor symptoms.

The study analyzed data from over 80 previous studies spanning the last five decades, aiming to establish reliable markers of disease asymmetry. Future directions involve refining methods to measure this asymmetry objectively and exploring whether similar patterns are observable in other neurodegenerative disorders linked to Parkinson’s.

Understanding the influence of the affected side on disease progression paves the way for more precise and individualized care, ultimately improving outcomes for patients living with Parkinson’s disease.

Source: https://medicalxpress.com/news/2025-07-parkinson-disease-affected-side.html