The relationship between cognitive task and postural stability in the early stages of Parkinson's disease

The Relatıonshıp Between Cognıtıve Task And Postural Stabılıty In The Early Stages Of Parkınson's Dısease Introduction: Parkinson's disease is an adult-onset progressive, neurodegenerative disease with an unclear etiopathogenesis. Postural instability is one of the disabling, cardinal symptoms of Parkinson's disease ocurring in advanced stages. The aim of this study is to examine the presence of dual task interference with cognitive tasks on postural stability in early stages of Parkinson's disease. Material and Methods: Thirty early-stage Parkinson's disease patients with a disease duration of at most five years, followed at Movement Disorders Unit of Neurology Department, Çukurova University and 20 age and sex-matched healty controls were enrolled in this prospective study. Neurological examination and minimental state examination were performed in all subjects. In order to determine the degree of disability in patients, Unified Parkinson Disease Rating Scale and Hoehn & Yahr scores were recorded. Balance control was assessed under several conditions (eyes open, eyes closed, mathematical and verbal cognitive tasks) using a static posturography in patients when they are "on" and in controls. The changes in total body sway, lateral sway, anterior-posterior sway, sway area and their velocities, as well as the Romberg coefficient were analysed. The SPSS22 was used for statistical analysis. Results: There were no statistically significant difference in any of the posturographic measures between patients and the control group with eyes open, eyes closed and secondary cognitive tasks. All posturographic parameters with eyes closed were statistically different from the measures with eyes open in both the patient and the control group. Similarly, all posturographic measures, except lateral sway, increased significantly with cognitive tasks compared to the ones with eyes open in both groups; however, the only difference from the control group was the significant increase in sway area with mathematical task in the patient group (p< 0.05). As for the correlation analysis, age correlated with lateral sway (r:0,370, p:0,044) and sway area during verbal cognitive tasks (r:0,385, p:0,036) in patients. Unified Parkinson Disease Rating Scale motor scores correlated with same of the sway parameters with both eyes open and eyes closed. They also correlated with sway area (r:0,447; p:0,013) and velocity of sway area (r:0,469, p:0,009) under mathematical cognitive task. Conclusions: Secondary cognitive tasks did not significantly affect postural stability in the early stages of Parkinson's disease in this study. Postural stability occurs with an integration of visual, vestibular and proprioceptive systems. If only two of these three systems are healthy, it will be enough for a normal balance control. On the other hand, the results of this study suggest that visual inputs are more influential on balance in this age group of subjects than expected. The correlation of age with many sway parameters in both controls and patients suggests that with advancing age there could be latent, subclinical proprioceptive and/or vestibular defects and this might have magnified the effect of visual system in this age group. In Parkinson's disease patients, other than age, advancing motor scores correlated with an increase in postural sway.Cognitive tasks effected postural sway in association with both advancing age and disease. Another point that should not be missed is the possible effect of dopaminergic therapy on the posturographic results. It is a well-known fact that the motor symptoms of early-stage Parkinson's disease respond well to dopaminergic therapy, probably including subclinical postural instability in this case. In conclusion, our findings suggest that in early- stage PD, cognitive tasks could affect postural stability depending on the age, the motor scores and the duration of the task. Key Words: Dual task interference, cognitive task, Parkinson's disease, postural instability, static posturography, Romberg coefficient.