Structural differences in impaired verbal fluency in essential tremor patients compared to healthy controls

Objective: We wanted to identify differences in grey and white matter in essential tremor patients compared to controls in the non-motor domain, using the example of impaired verbal fluency.

Background: A disturbance of verbal fluency in essential tremor patients compared to healthy controls is behaviorally well described.

Methods: Voxel-based morphometry and tract-based spatial statistics were used to analyze structural differences in grey and white matter in 19 essential tremor patients compared to 23 age- and gender-matched controls.

Results: Several significant observations were made. (I) There was less grey matter in the predominantly right precuneus in the essential tremor group compared to controls [p < .001]. (II) In ET patients mean, axial, and radial diffusivity values broadly correlated with the tremor rating scale, pronounced in fronto-parietal regions [p < .05]. (III) In ET patients there was a significant decline in fractional anisotropy values in the corpus callosum in the correlation with verbal fluency results [p < .05]; by inclusion of the tremor rating scale as covariate of no interest this significance was however diminished to a tendency (p < .1). No significant results were found in these within-group correlations in grey matter analyses for ET patients (p > .05).

Conclusion: The present results indicate that non-motor symptoms such as verbal fluency (VBF) in ET have a structural substrate; their reproduction requires the integration of potential environmental plasticity effects, differentiation into individual clinical subtypes and a careful handling with methodological peculiarities of structural MR imaging.