Differential impact on speech production from chronic thalamic DBS in Essential Tremor and that from STN DBS in Parkinson's disease

Essential Tremor (ET) is the most common tremor syndrome seen in adults. The characteristic tremor in ET is postural and action tremors, with a frequency of 4–7 Hz; while in patients with Parkinson’s disease (PD), the dominant tremor is resting tremor with a typical frequency of 5 Hz. Deep brain stimulation (DBS) in the ventral intermediate nuclei (Vim) has been shown effective in treating action or intention tremors in medically resistant ET, while DBS in the subthalamic nucleus (STN) has been shown effective in treating rigidity, rest tremor and Dopa-induced dyskinesias in PD. However, chronic bilateral DBS, whether in Vim or STN, may have negative impact on speech production. We report two cases where both patients received DBS greater than one year and developed speech impairment. When the stimulation in Vim was turned off for 30 min in ET, the patient's speech returned to the baseline while turning the STN stimulation off for 30 min in PD, minimal changes were observed and 12 h with stimulation-off were required for speech to return to the non-stimulated state.Essential Tremor (ET) is the most common tremor syndrome seen in adults. The characteristic tremor in ET is postural and action tremors, with a frequency of 4–7 Hz; while in patients with Parkinson’s disease (PD), the dominant tremor is resting tremor with a typical frequency of 5 Hz. Deep brain stimulation (DBS) in the ventral intermediate nuclei (Vim) has been shown effective in treating action or intention tremors in medically resistant ET, while DBS in the subthalamic nucleus (STN) has been shown effective in treating rigidity, rest tremor and Dopa-induced dyskinesias in PD. However, chronic bilateral DBS, whether in Vim or STN, may have negative impact on speech production. We report two cases where both patients received DBS greater than one year and developed speech impairment. When the stimulation in Vim was turned off for 30 min in ET, the patient's speech returned to the baseline while turning the STN stimulation off for 30 min in PD, minimal changes were observed and 12 h with stimulation-off w...