015-22 – Regional cerebellar morphometric alterations in early Parkinson’s disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease primarily characterised by progressive basal ganglia degeneration. Growing evidence suggests areas outside the basal ganglia are also impacted, particularly regions involved in motor functions. We aimed to quantify the volume of individual cerebellar lobules on MRI scans in patients with a new diagnosis of PD to determine cerebellar alterations earlier in the disorder and whether changes relate to principle symptomatic features.
We studied patients with PD (PwP) and healthy controls (HC) enrolled into the Parkinson’s disease progressive markers initiative. PwP were stratified into tremor-dominant (TD) and postural instability gait difficulty (PIGD) motor phenotype based on UPDRS-III motor assessment scores. We used automatic cerebellum anatomical parcellation using U-Net with locally constrained optimization (ACAPULCO) to parcellate the cerebellum (figure 1). ACAPULCO parcellated 238 PwP to analyse symptom related cerebellar changes and a further 107 HC to analyse disease related cerebellar changes. Permutation analysis of linear models was used to calculate these differences and family wise error corrections applied.

PwP had a significant volume increase of the right (t=3.14, pFWE=0.008) and left (t=2.92, pFWE=0.016) cerebellar lobule V, and a strong trend for increased volume of the right VI lobule in patients (t=2.29, pFWE=0.088). There were no significant differences in cerebellar lobule volume between TD and PIGD motor subtypes.
We present evidence indicating that constituent regions of the cerebellum involved in motor control are enlarged in the early stages of PD. This new finding is consistent with previous functional MRI and positron emission tomography studies, indicating regional cerebellar hyperactivity and glucose hypermetabolism as part of a potential compensatory mechanism. We are now examining cerebellar volumes change over time in PwP as part of a longitudinal study.