Corpus Callosum Structural Alterations in Essential Tremor with and Without Resting Tremor: A Multimodal MRI Study.

Background: Essential tremor (ET) is a common movement disorder characterized by postural and kinetic tremor. Some patients also show resting tremor, being classified as the ET-plus distinct subtype. The corpus callosum (CC) involvement is proven in several neurological diseases, including ET, but differences between ET with and without resting tremor have not been studied. In this study, we investigated structural characteristics of the CC in a cohort of ET and ET with resting tremor (ETrt) patients, compared to healthy controls (HC). Methods: We enrolled 128 participants (63 ET, 38 ETrt, and 27 HC). We performed a multimodal MRI evaluation (thickness, mean diffusivity [MD], and fractional anisotropy [FA]) of the CC's genu, body, and splenium, using different statistical approaches. We first performed a traditional group-based comparison, controlling for relevant covariates. Then, we used an unsupervised classification model based on MRI data to explore potential subgroup distinctions. Results: Our evaluation showed significant changes in structural parameters of CC in both ET and ETrt patients compared to HC, mainly represented by thickness reductions across all regions and MD increase in the body. Notably, we found no differences between the ET and ETrt groups. Clustering analysis reinforced this observation, placing ET and ETrt in a single cluster with similar abnormalities in all MRI parameters and clearly separating them from HC. Discussion: Despite their clinical differences, ET with and without resting tremor patients showed analogous macro- and microstructural changes in the CC, suggesting shared pathophysiological processes within this brain region. Highlights: We explored structural integrity of the Corpus Callosum in ET patients with and without resting tremor. We found a thinning of the corpus callosum and microstructural abnormalities overlapping in ET and ETrt groups, suggesting that despite their different clinical presentations, they share some underlying mechanisms.