Longitudinal study of clinical and neurophysiological features in essential tremor

Background and purpose: Essential tremor (ET) is a common and heterogeneous disorder characterized by postural/kinetic tremor of the upper limbs and other body segments and by non--motor symptoms, including cognitive and psychiatric abnormalities. Only a limited number of longitudinal studies have comprehensively and simultaneously investigated motor and non--motor symptom progression in ET. Possible soft signs that configure the ET--plus diagnosis are also under--investigated in follow--up studies. We aimed to longitudinally investigate the progression of ET manifestations by means of clinical and neurophysiological evaluation. Methods: Thirty--seven ET patients underwent evaluation at baseline (T0) and at follow-up ( T1; mean interval +/- SD = 39.89 +/- 9.83 months). The assessment included the clinical and kinematic evaluation of tremor and voluntary movement execution, as well as the investigation of cognitive and psychiatric disorders. Results: A higher percentage of patients showed tremor in multiple body segments and rest tremor at T1 as compared to T0 (all p--values < 0.01). At T1, the kinematic analysis revealed reduced finger--tapping movement amplitude and velocity as compared to T0 (both p--values < 0.001). The prevalence of cognitive and psychiatric disorders did not change between T0 and T1. Female sex, absence of family history, and rest tremor at baseline were identified as predictive factors of worse disease progression. Conclusions: ET progression is characterized by the spread of tremor in multiple body segments and by the emergence of soft signs. We also identified possible predictors of disease worsening. The results contribute to a better understanding of ET classification and pathophysiology.