Morphometric and functional MRI changes in essential tremor with and without resting tremor

The etiopathogenesis of essential tremor (ET) is still debated, since the predominant role of circuit dysfunction or brain degenerative changes has not been clearly established. The relationship with Parkinson's Disease (PD) is also controversial and resting tremor occurs in up to 20 % of ET. We investigated the morphological and functional changes associated with ET and we assessed potential differences related to the presence (ET+R) or absence (ET-R) of resting tremor. 32 ET patients (18 ET+R; 14 ET-R) and 12 healthy controls (HC) underwent 3T-MRI protocol including Spoiled Gradient T1-weighted sequence for Voxel-Based Morphometry (VBM) analysis and functional MRI during continuous writing of "8" with right dominant hand. VBM analysis revealed no gray and white matter atrophy comparing ET patients to HC and ET+R to ET-R patients. HC showed a higher BOLD response with respect to ET patients in cerebellum and other brain areas pertaining to cerebello-thalamo-cortical circuit. Between-group activation maps showed higher activation in precentral gyrus bilaterally, right superior and inferior frontal gyri, left postcentral gyrus, superior and inferior parietal gyri, mid temporal and supramarginal gyri, cerebellum and internal globus pallidus in ET-R compared to ET+R patients. Our findings support that the dysfunction of cerebello-thalamo-cortical network is associated with ET in absence of any morphometric changes. The dysfunction of GPi in ET+R patients, consistently with data reported in PD resting tremor, might suggest a potential role of this structure in this type of tremor.