Orthostatic tremor is a rare movement disorder characterized by a sensation of unsteadiness and leg tremor while standing. It has been hypothesized that the disorder is attributable to dysregulation of a central oscillatory network in the brain. This putative network includes primary motor cortex, supplementary motor area, cerebellum, thalamus, and pontine tegmentum. We studied this brain network by recording resting-state functional MRI data from individuals with orthostatic tremor. For each participant, we measured resting-state functional connectivity using a seed-based approach. Regions of interest included were components of the putative central oscillatory network and a primary motor thumb region (identified via transcranial magnetic stimulation). A non-central oscillatory network region of interest-posterior cingulate cortex-was included for comparative analysis of a well-characterized intrinsic network, the default mode network. Demographic information, medical history, and tremor characteristics were collected to test associations with functional connectivity. For normative context, data from the 1000 Functional Connectomes Project were analyzed using an identical approach. We observed that tremor and demographic variables were correlated with functional connectivity of central oscillatory network components. Furthermore, relative to healthy comparison participants, patients with orthostatic tremor exhibited qualitatively different patterns of cerebellar resting state functional connectivity. Our study enhances the current understanding of brain network differences related to orthostatic tremor and is consistent with a hypothesized selective decoupling of cerebellum. Additionally, associations observed between functional connectivity and factors including medical history and tremor features may suggest targets for treatment of orthostatic tremor.

May 5, 2019April 9, 2019Free AccessOutcomes of Deep Brain Stimulation Surgery in Parkinson’s Disease: Real Life Experience from a Tertiary Care Center (P1.8-038)Ryan Brennan, David Whitney, Amy Hellman, John M. Bertoni, Diego Torres-Russotto, and Danish BhattiAuthors Info & AffiliationsApril 9, 2019 issue92 (15_supplement)https://doi.org/10.1212/WNL.92.15_supplement.P1.8-038 Letters to the Editor

Orthostatic tremor (OT) is a rare movement disorder characterized by a fast tremor (13-18 Hz) in the lower extremities during stance. Patients with OT typically complain of instability while standing/walking. However, due to the geographical limitation, the standing instability or gait problems in patients with OT cannot be assessed and monitored frequently. The increasing popularity of using smartphone-based accelerometers could be a solution to eliminate this limitation. This study examined the feasibility of using smartphone-based accelerometers to identify the changes in body movement in different standing and locomotor tasks. Twenty patients with OT and seven healthy controls were consented to participate in this study. Subjects stood with eyes open or eyes closed for 20 seconds. They also performed four different locomotor tasks (normal walking, tandem walk, walking on an elevated surface, and obstacle negotiation). When performed different locomotor tasks, patients with OT had a larger acceleration of body movement than controls in the medial-lateral direction (tandem walk: p = 0.026, walking on an elevated surface: p = 0.002, and stepping over the obstacle: p = 0.028). Patients with OT had smaller acceleration of body movement than controls while standing with eyes open in the vertical direction (p = 0.012), in the anterior-posterior direction (p = 0.013) and in the medial-lateral direction (p = 0.011). This study provides objective evidence of balance instability in patients with OT not only while standing but also during different challenging locomotor tasks by using smartphone-based accelerometers.

Purpose of review Orthostatic tremor (OT) is a rare disorder characterized by tremor and a feeling of unsteadiness while standing that resolve upon walking or sitting. A pathognomonic 13–18 Hz tremor is seen on surface EMG while standing. Though its clinical features have been better defined over time, much of its pathophysiology remains unknown and treatment options are limited. We review here recent developments in both of these areas. Recent findings Several recent studies have furthered our understanding of the central oscillatory network involved in OT. fMRI and 18 F-FDG-PET studies have identified a ponto-cerebello-thalamo-cortical network underlying OT, though the nature of its dysfunction remains unknown. Randomized trials of treatments for OT are few, so most data are from case reports or small case series. Clonazepam and gabapentin are likely the most effective medical therapies, while bilateral ventral intermediate nucleus deep brain stimulation shows promise for refractory cases. Summary Though much about OT remains unknown, our understanding of its pathophysiology has improved through recent studies. Treatment benefit is overall modest and inconsistent, though better understanding of the disease could lead to new avenues for treatment.

Drug-induced parkinsonism is well understood to be caused by chronic exposure to dopamine-blocking agents. These include typical and so-called “atypical” antipsychotics, anti-nausea medications such as metoclopramide and prochlorperazine, and others. Drug-induced parkinsonism usually improves or completely resolves after removal of the causative agent, though these effects might rarely be irreversible. In these cases the term tardive parkinsonism has been used, though the existence of this as a distinct clinical entity is controversial.