Striatal compartment and white matter alterations in focal dystonia Subtypes: An MRI study

Dystonia is a movement disorder marked by involuntary muscle contractions that cause abnormal postures or repetitive movements. The striatum plays a key role in motor control and is central to dystonia pathophysiology. Recent advances in diffusion MRI enable in vivo parcellation of the striatum into matrix- and striosome-like compartments, associated with sensorimotor and limbic functions. We aimed to assess structural brain differences between focal dystonia patients and healthy controls (HC) using T1-weighted and diffusion MRI, and to explore subtype-specific alterations in striatal compartments.

We analyzed 3T MRI data from 91 participants: 29 with upper limb dystonia (ULD), 25 with cervical dystonia (CD), and 37 HCs. T1-weighted images were processed using FreeSurfer for morphometry; diffusion data underwent tractography-based striatal parcellation and TBSS using FSL. Group comparisons were performed with PALM, adjusting for age, sex, and multiple comparisons.

Compared to HCs, dystonia patients (ULD + CD) showed reduced volume in the left caudate and matrix-like voxels. Putaminal volume inversely correlated with symptom severity. CD patients had reduced volume in the right thalamus and left caudate and globus pallidus. ULD patients showed reduced matrix-like and increased striosome-like volume in the left striatum. CD patients also had increased radial diffusivity in the right corona radiata and mean diffusivity in the corpus callosum. No cortical differences were observed.

Our findings highlight distinct neuroanatomical patterns in focal dystonia subtypes, with cervical dystonia showing widespread subcortical and white matter alterations, and upper limb dystonia presenting a striatal compartment imbalance, suggesting divergent pathophysiological mechanisms.