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.