Objective: To report the statistical analyses exploring the association between BMI and change in Unified Parkinson’s disease Rating Scale (UPDRS) scores and survival in the NET-PD LS1.

Background: BMI is associated with survival in Huntington’s disease and Amyotrophic Lateral Sclerosis, but its association with survival in Parkinson’s disease is unknown.

Methods: Secondary analysis of longitudinal data from 1673 participants in NET-PD LS1. Outcomes: (i) change in motor and (ii) total UPDRS scores and (iii) survival. Exposure: BMI at randomization and change in BMI trajectory groups. Trajectory groups identified via a semi-parametric group-based model with continuous multivariate density functions under a censored normal model. Participants were categorized into decreasing change in BMI, stable change in BMI, or increasing change in BMI. Generalized linear mixed models (GLMM) were used to estimate the effect of the change in BMI trajectory group on outcomes (i) and (ii). Survival was analyzed using Cox proportional hazards models of time to death. A sensitivity analysis using GLMM were conducted to estimate the effect of change in BMI on the change in UPDRS scores.

Results: The decreasing BMI group increased by 1.48 (S.E. 0.28, p<0.001) more points per visit in the motor UPDRS than participants classified in the stable BMI group. The increasing BMI group increased by -0.51 (S.E. 0.24, p=0.03) fewer points per visit. The trajectory analysis and the sensitivity analysis reached similar results. The change in BMI trajectory groups was not significant associated with survival.

Conclusions: Although change in BMI was associated with change in UPDRS scores, causality cannot be evaluated. We recommend the creation of the BMI trajectories as a cleaner approach to disentangle this association.

This abstract is part of the accepted publication: Wills, A.M., Pérez A, Wang, J., Su, X., Morgan, J., Rajan, S.S., Leehey, M., Pontone, G.M., Chou, K., Umeh, C., Mari,Z., Boyd, J. for the NINDS Exploratory Trials in Parkinson’s disease (NET-PD) Investigators (2015) Association Between Change in Body Mass Index, Unified Parkinson’s disease Rating Scale Scores, and Survival Among Persons With Parkinson’s disease. Secondary Analysis of Longitudinal Data From NINDS Exploratory Trials in Parkinson’s disease Long-term Study 1. JAMA Neurology. Accepted November 3, 2015.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/statistical-aspects-when-exploring-the-association-between-change-in-body-mass-index-bmi-updrs-scores-and-survival-in-the-net-pd-long-term-study-1/