Perceived imbalance and risk of Parkinson's disease.

We prospectively examined associations between perceived imbalance and Parkinson's disease (PD) risk in the Health Professional Follow-up Study (HPFS), and Nurses' Health Study (NHS). We included 39,087 men and 82,299 women free of PD at baseline (1990) in the current analyses. We documented 449 incident PD cases during 12 years follow-up. Subjects who reported difficulty with balance before 1990 (baseline) were 1.8 more times likely to develop PD, relative to those who reported no balance difficulty (pooled multivariate RR = 1.8; 95% CI: 1.3, 2.5; P < 0.0001). When we further examined associations between perceived imbalance at baseline and PD onset during different time periods, we found a significant elevation of PD risk only during the first 4 years of follow-up. This result suggests that the imbalance may in some cases be an early sign of PD, and may represent the onset of motor symptoms although they have not been clinically recognized. (c) 2008 Movement Disorder Society.