E020 Volumetric change across the different stages of the Huntington’s disease integrated staging system (HD-ISS) defined at baseline

<h3>Background</h3> The HD-ISS enables classification of people with HD into four disease stages. Here we characterized volume atrophy in the caudate nucleus, putamen and whole-brain across the HD-ISS Stages and compared to healthy controls (HC). <h3>Methods</h3> We used data from the HD Imaging Harmonisation consortium (HD-IH), employing the IXIQ.Ai analysis pipeline. IXIQ.Ai cut-offs for HD-ISS Stage 1 are in progress, we therefore we couldn’t distinguish between Stages 0 and 1 and combined them into Stage 0/1 (table 1). We fit linear mixed models with random intercepts and slopes with volume (normalized for head size) as the outcome. Predictors of interest were baseline group (4 levels) and its interaction with time (in years). Models were adjusted for sex, field strength, site, baseline age and their interactions with time. <h3>Results</h3> For all regions, there was a significant main group effect and group by time interaction, such that the HC had the largest volumes and slowest rate of change (all p&lt;0.001). Post-hoc comparisons between the HD-ISS groups, showed that as Stage increased mean volume decreased significantly for all regions. For rate of change the whole-brain showed a similar pattern of stage-related increase, whereas for the caudate Stage 2 had greater rate of change than Stage 0/1, but no different from Stage 3. For the putamen, Stage 2 had greater rate of change than both Stage 0/1 and 3 (figure 1). <h3>Conclusion</h3> Our analyses show that rate of volume change differs across the HD-ISS Stages and the pattern of change differs between regions.