Orthostatic tremor and I123-FP-CIT-SPECT: report of a case

Pathogenesis of Primary Orthostatic Tremor: Current Concepts and Controversies

Background

Orthostatic tremor (OT), a rare and complex movement disorder, is characterized by rapid tremor of both legs and the trunk while standing. These disappear while the patient is either lying down or walking. OT may be idiopathic/primary or it may coexist with several neurological conditions (secondary OT/OT plus). Primary OT remains an enigmatic movement disorder and its pathogenesis and neural correlates are not fully understood.

Methods

A PubMed search was conducted in July 2017 to identify articles for this review.

Results

Structural and functional neuroimaging studies of OT suggest possible alterations in the cerebello-thalamo-cortical network. As with essential tremor, the presence of a central oscillator has been postulated for OT; however, the location of the oscillator within the tremor network remains elusive. Studies have speculated a possible dopaminergic deficit in the pathogenesis of primary OT; however, the evidence in favor of this concept is not particularly robust. There is also limited evidence favoring the concept that primary OT is a neurodegenerative disorder, as a magnetic resonance spectroscopic imaging study revealed significant reduction in cerebral and cerebellar N-acetyl aspartate (NAA) levels, a marker of neuronal compromise or loss.

Discussion

Based on the above, it is clear that the pathogenesis of primary OT still remains unclear. However, the available evidence most strongly favors the existence of a central oscillatory network, and involvement of the cerebellum and its connections.

Orthostatic tremor: current challenges and future prospects

This review provides an outlook of orthostatic tremor (OT), a rare adult-onset tremor characterized by subjective unsteadiness during standing that is relieved by sitting or walking. Recent case series with a long-time follow-up have shown that the disease is slowly progressive, spatially spreads to the upper limbs, and other neurological disorders may develop in about one-third of the patients. The diagnosis of OT hinges on the typical history of unsteadiness during standing, which is confirmed by electromyographic findings of a 13–18 Hz tremor that is typically absent during tonic activation while the patient is sitting and lying. Although the tremor is generated by a central oscillator, cerebellar and/or basal ganglia dysfunction are needed for its manifestation (double lesion hypothesis). However, functional neuroimaging findings have not consistently implicated the dopaminergic system in its pathogenesis. Drug treatments have been largely disappointing with no sustained benefits, although thalamic deep brain stimulation has helped some patients. Large-scale follow-up studies, more drug trials, and novel therapies are urgently needed.

The long-term outcome of orthostatic tremor

OBJECTIVES

Orthostatic tremor is a rare condition characterised by high-frequency tremor that appears on standing. Although the essential clinical features of orthostatic tremor are well established, little is known about the natural progression of the disorder. We report the long-term outcome based on the largest multicentre cohort of patients with orthostatic tremor.

METHODS

Clinical information of 68 patients with clinical and electrophysiological diagnosis of orthostatic tremor and a minimum follow-up of 5 years is presented.

RESULTS

There was a clear female preponderance (76.5%) with a mean age of onset at 54 years. Median follow-up was 6 years (range 5-25). On diagnosis, 86.8% of patients presented with isolated orthostatic tremor and 13.2% had additional neurological features. At follow-up, seven patients who initially had isolated orthostatic tremor later developed further neurological signs. A total 79.4% of patients reported worsening of orthostatic tremor symptoms. These patients had significantly longer symptom duration than those without reported worsening (median 15.5 vs 10.5 years, respectively; p=0.005). There was no change in orthostatic tremor frequency over time. Structural imaging was largely unremarkable and dopaminergic neuroimaging (DaTSCAN) was normal in 18/19 cases. Pharmacological treatments were disappointing. Two patients were treated surgically and showed improvement.

CONCLUSIONS

Orthostatic tremor is a progressive disorder with increased disability although tremor frequency is unchanged over time. In most cases, orthostatic tremor represents an isolated syndrome. Drug treatments are unsatisfactory but surgery may hold promise.