Objective: To evaluate potential differences in cognitive, motor and demographic factors between individuals who are lost to follow-up in the longitudinal Tuebinger evaluation of Risk factors for Early detection of NeuroDegeneration (TREND) study, which focusses on the development of Parkinson’s and Alzheimer’s disease.

Background: Longitudinal studies are essential for the investigation of prodromal markers and risk factors of neurodegenerative diseases, such as Parkinson’s and Alzheimer’s disease. Here, individuals diagnosed with these diseases over time are commonly compared to individuals who remain healthy. Yet, little is known about the characteristics of participants who drop out over the course of these studies potentially introducing biases into prodromal and risk marker analyses.

Methods: A total of 1138 healthy elderly individuals participated in the prospective biennial TREND study investigating the prodromal/risk markers for the early detection of neurodegeneration. Cognitive performance in domains of memory, language, visuo-spatial, and executive functions (CERAD-Plus neuropsychological battery), age, gender and years of education as well as worsening of motor function (UPDRS-III) at the baseline visit were compared between individuals remaining in the study for at least two visits (non drop-outs) and those lost to follow-up. Kruskal-Wallis tests were used for group comparison.

Results: In total, the 184 (16.2%) drop-outs showed significantly lower cognitive performance in memory and executive functions (p<.001), but not in language and visuo-spatial (p>.1) performance (z-values corrected for age, gender and education) compared to non drop-outs. Drop-outs were older (p<.001) and less educated (mean difference: p=0.001), but did not differ in gender composition. Motor performance as indicated by the UPDRS-III was lower in drop-outs compared to non-drop-outs (mean differences, p<.001).

Conclusions: Individuals lost to follow-up are according to these findings more prone to a future diagnosis of a neurodegenerative diseases compared to non drop-outs. This may introduce considerable biases to the analyses of prodromal marker effects. Strategies to increase retention rates in longitudinal studies should consider the present findings and focus from the beginning on also retaining those who perform less well with regard to motor and cognitive function.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/characteristics-of-drop-outs-in-a-longitudinal-study-on-individuals-at-risk-for-a-neurodegenerative-disorder/