Regionally, distinctive white matter microstructural values in patients with essential tremor (ET) localize to the cerebellar peduncles and thalamo-cortical visual pathways, a recent study found. These findings complement recent functional imaging studies in ET but also extend the understanding of putative physiologic features that account for distinctions between ET and Parkinson disease (PD). Sedated participants with ET (n=57) or PD (n=99) underwent diffusion tensor imaging (DTI); fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity values were computed. White matter tracts were defined using 3 well-described atlases. Researchers found:

• Fractional anisotropy values that differentiate ET from PD localize primarily to thalamic and visual-related pathways, while diffusivity differences localized to the cerebellar peduncles.
• Patients with ET exhibited lower fractional anisotropy values than patients with PD in the lateral geniculate body, sagittal stratum, forceps major, pontine crossing tract, and retrolenticular internal capsule.
• Patients with ET exhibited greater radial diffusivity values than patients with PD in the superior cerebellar peduncle, middle cerebellar peduncle, and inferior cerebellar peduncle.