Postural Sway as a Measure of Disease Severity in Parkinson's Disease

Introduction The severity of Parkinsons disease (PD) is difficult to assess accurately owing to the lack of a robust biological marker of disease progression, with consequent implications for prognosis and treatment. The current standard measure is the Unified Parkinsons Disease Rating Scale (UPDRS) but this is hampered by considerable variability between observers and within subjects. Postural sway correlates well with complex brain functioning in other conditions. This study aimed to investigate the correlation of postural sway with the UPDRS and other non-motor measures of disease severity in patients with PD. Methods 28 patients with PD (mean age 68 years, range 5491; 18 male) underwent tests of cognition and quality of life [Montreal Cognitive Assessment (MoCA), Neuropsychiatry Unit Cognitive Assessment (NUCOG) and Parkinsons Diseases Questionnaire (PDQ-391)], assessment of postural sway using a force plate, and assessment of clinical status using the motor component of the UPDRS. Results Sway path length showed strong correlations with PDQ-391, MoCA and the verbal fluency component of the NUCOG (r=0.63,0.75 and −0.57, respectively; p=0.002,<0.001and 0.002, respectively) and, to a lesser degree, with the UPDRS III (r=0.45, p=0.018). Conclusion Postural sway shows potential as a sensitive measure of disease severity and brain function in PD, either alone or in combination with other measures. It appears to correlate better with measures of cognition, both general and executive (verbal fluency), and the PDQ measure of disease severity than with the motor component of the UPDRS.