Orthostatic Tremor and Orthostatic Myoclonus: Weight-bearing Hyperkinetic Disorders: A Systematic Review, New Insights, and Unresolved Questions

Utility of Neurophysiological Evaluation in Movement Disorders Clinical Practice

Background

Quantitative and objective neurophysiological assessment can help to define the predominant phenomenology and provide diagnoses that have prognostic and therapeutic implications for movement disorders.

Objectives

Evaluate the agreement between initial indications and final diagnoses after neurophysiological evaluations in a specialized movement disorders center.

Methods

Electrophysiological studies conducted for movement disorders from 2003 to 2021 were reviewed. The indications were classified according to predominant phenomenology and the diagnoses categorized in subgroups of phenomenology.

Results

A total of 509 studies were analyzed. 51% (259) of patients were female, with a mean age of 51 years (ranges 5 to 89 years). The most common reasons for referral were evaluation of functional movement disorders (FMD), followed by jerky movements, tremor and postural instability. Regarding FMD referrals, there was a diagnostic change in 13% of the patients after electrophysiological assessment. The patients with jerky movements as indication had a diagnosis other than myoclonus in 27% of them, and tremor was not confirmed in 20% of the cases. In patients with an electrophysiological diagnosis of FMD, it was not suspected in 30% of the referrals. Similarly, tremor was not mentioned in the referral of 17% of the patients with this electrophysiological diagnosis and myoclonus was not suspected in 13% of the cases.

Conclusions

Electrophysiological assessment has utility in the evaluation of movement disorders, even in patients evaluated by movement disorders neurologists. More studies are needed to standardize the protocols between centers and to promote the availability and use of these techniques among movement disorders clinics.

Orthostatic tremor after knee contusion without head trauma: A rare case report

Orthostatic tremor (OT) is an uncommon progressive movement disorder that involves a leg tremor when standing or weight bearing. Additionally, OT can accompany other medical or neurodegenerative disorders. In this article, we report an unusual case of OT after trauma in an 18-year-old male patient whose symptoms of OT have been resolved after a multimodal therapeutic approach, including botulinum toxin injection. Surface electromyography, including a tremor recording, was used for the diagnosis of OT. The patient completely recovered after the rehabilitation. A comprehensive rehabilitative treatment is required in the management of OT as the patient's quality of life is greatly affected.

Video electroencephalogram combined with electromyography in the diagnosis of hyperkinetic movement disorders with an unknown cause

OBJECTIVES

Diagnosis of hyperkinetic movement disorders with an unknown cause is usually challenging. The objective of this study is to learn about video electroencephalogram (VEEG) combined with electromyography (EMG) in the diagnosis of hyperkinetic movement disorders with an unknown cause.

METHODS

We performed an observational cohort study by recruiting consecutive patients with hyperkinetic movements as the main manifestation with an unknown cause for VEEG combined with EMG evaluations.

RESULTS

A total of 77 consecutive patients were enrolled for VEEG-EMG examination. Among them, 57 patients changed their diagnosis after VEEG-EMG assessment, with a mean final diagnosis age of 35.4 ± 20.3 years (range, 4-74 years). The mean duration between initial and final diagnosis was 54.8 ± 71.3 months (range 0.5-300 months). The most common misdiagnosed hyperkinetic movement disorders were myoclonus (40.4%), followed by tremors (24.6%), dystonia (15.8%), psychogenic movement disorders (10.5%), and periodic leg movement syndrome (PLMS) (7.0%). Outcomes of therapy were significantly improved after VEEG-EMG examination (p = 0.000).

CONCLUSIONS

Simultaneous VEEG and EMG are important in the diagnosis of hyperkinetic movement disorders with an unknown cause.

Deep brain stimulation for orthostatic tremor: A single-center case series

Background

Orthostatic tremor (OT) is a high-frequency weight-bearing tremor of the legs and trunk associated with progressive disability and is often refractory to medications. Case reports suggest that thalamic deep brain stimulation (DBS) is effective. We report 5 female patients with medication-refractory OT who underwent bilateral thalamic DBS at the Mayo Clinic and assess factors associated with a successful DBS outcome.

Methods

Demographic, clinical, electrophysiology, and DBS data were abstracted. Outcomes were change in tremor-onset latency, standing time, standing ADLs, and patient and clinician global impression of change (PGIC; CGIC).

Results

All 5 patients had improved standing time (72 vs 408 seconds, p ≤ 0.001) and improved standing ADLs after surgery, without change in tremor-onset latency (16 vs 75 seconds, p = 0.14). Maximal benefit was reached up to 3 years after surgery and sustained for up to 6 years. CGIC was "much improved" in all; PGIC was "much improved" in 4 and "minimally improved" in 1. There were no major complications. Postoperative electrophysiology (n = 1) showed lower tremor amplitude and slower tremor ramp-up on vs off stimulation.

Conclusions

Bilateral thalamic DBS improved OT symptoms with benefit lasting up to 6 years. A modest increase in standing time of several minutes was associated with meaningful improvement in standing ADLs. Microlesional effect and bilateral stimulation are likely favorable features, while baseline standing time of several minutes may be unfavorable. These findings may inform clinician and patient counseling and require confirmation in larger studies.

Myoclonus: An Electrophysiological Diagnosis

Background

Many different movement disorders have similar "jerk-like" phenomenology and can be misconstrued as myoclonus. Different types of myoclonus also share similar phenomenological characteristics that can be difficult to distinguish solely based on clinical exam. However, they have distinctive physiologic characteristics that can help refine categorization of jerk-like movements.

Objectives

In this review, we briefly summarize the clinical, physiologic, and pathophysiologic characteristics of different types of myoclonus. The methodology and technical considerations for the electrophysiologic assessment of jerk-like movements are reviewed. A simplistic pragmatic approach for the classification of myoclonus and other jerk-like movements based on objective electrophysiologic characteristics is proposed.

Conclusions

Clinical neurophysiology is an underutilized tool in the diagnosis and treatment of movement disorders. Various jerk-like movements have distinguishing physiologic characteristics, differentiated in the milliseconds range, which is beyond human capacity. We argue that the categorization of movement disorders as myoclonus can be refined based on objective physiology that can have important prognostic and therapeutic implications.

Levodopa-Responsive Primary Slow Orthostatic Tremor: A Premotor Sign of Parkinson's Disease?

We present a case of primary orthostatic tremor (OT) responsive to dopaminergic medication. The patient was a 62-year-old woman, who had leg tremor on standing for 2 years. No parkinsonian or other neurological signs were observed. Surface electromyography of the quadriceps muscles showed regular 5–6 Hz muscle discharges. [¹²³I]-FP-CIT DAT-SPECT imaging revealed decreased specific binding ratio values in the striatum compared with age-matched controls. Her leg tremor almost completely disappeared following administration of levodopa 200 mg and pramipexole 0.75 mg. Since her OT with low-frequency discharge was responsive to dopaminergic medication, we speculate that it may be a premotor sign of Parkinson's disease.

Principles of Electrophysiological Assessments for Movement Disorders

Electrophysiological studies can provide objective and quantifiable assessments of movement disorders. They are useful in the diagnosis of hyperkinetic movement disorders, particularly tremors and myoclonus. The most commonly used measures are surface electromyography (sEMG), electroencephalography (EEG) and accelerometry. Frequency and coherence analyses of sEMG signals may reveal the nature of tremors and the source of the tremors. The effects of voluntary tapping, ballistic movements and weighting of the limbs can help to distinguish between organic and functional tremors. The presence of Bereitschafts-potentials and beta-band desynchronization recorded by EEG before movement onset provide strong evidence for functional movement disorders. EMG burst durations, distributions and muscle recruitment orders may identify and classify myoclonus to cortical, subcortical or spinal origins and help in the diagnosis of functional myoclonus. Organic and functional cervical dystonia can potentially be distinguished by EMG power spectral analysis. Several reflex circuits, such as the long latency reflex, blink reflex and startle reflex, can be elicited with different types of external stimuli and are useful in the assessment of myoclonus, excessive startle and stiff person syndrome. However, limitations of the tests should be recognized, and the results should be interpreted together with clinical observations.

Slow Orthostatic Tremor: Review of the Current Evidence

Background

Orthostatic tremor (OT) is defined as tremor in the legs and trunk evoked during standing. While the classical description is tremor of ≥13 Hz, slower frequencies are recognized. There is disagreement as to whether the latter represents a slow variant of classical OT, or different tremor disorder(s) given frequent coexistent neurological disease.

Methods

A systematic literature search of PubMed was performed in February 2019 for “slow orthostatic tremor” and related terms which generated 573 abstracts, of which 61 were included.

Results

Between 1970 and 2019, there were 70 cases of electrophysiologically confirmed slow OT. Two-thirds were female, of mean age 60 years (range 26–86), and mean disease duration 6 years (range 0–32). One-third of cases were isolated, and two-thirds had a coexistent disorder(s), including parkinsonism (30%), ataxia (12%), and dystonia (10%). Postural arm tremor was present in 34%. Median tremor frequency was 6–7 Hz (range 3–12). Tremor bursts ranged from 50 to 150 ms duration, and were alternating or synchronous in antagonistic and/or analogous muscles. Low and high coherences were reported. Five cases (7%) had coexistent classical OT. Clonazepam was the most effective medication across all frequencies, and levodopa was effective for 4–7 Hz OT with coexistent parkinsonism. Two cases resolved with the treatment of Graves’ disease. Electrophysiology and imaging predominantly support a central tremor generator.

Discussion

While multiple lines of evidence separate slow OT from classical OT, clinical and electrophysiological overlap may occur. Primary and secondary causes are identified, similar to classical OT. Further exploration to clarify these slow OT subtypes, clinically and neurophysiologically, is proposed.

A Rare Presentation of Orthostatic Tremor as Abdominal Tremor

Background

Orthostatic tremor (OT) is a weight-bearing hyperkinetic disorder characterized by unsteadiness while standing that is relieved when sitting or walking.

Case report

A 66-year-old male presented with a 5 year-history of tremor in his abdomen, but only when he stood in a stationary position. The tremor disappeared when he stood or walked. On examination, he had palpable tremor in his rectus abdominis and gastrocnemius virtually instantaneously after standing. His electromyography findings confirmed the presence of a 12-Hz tremor in the tibialis anterior while standing, with subharmonics recorded in the external obliques and rectus abdominis.

Discussion

Our case illustrates an unusual presentation of OT. The diagnosis is supported by its characteristic frequency and specific appearance only during upright stance.

Myoclonic Disorders

Few movement disorders seem to make a straightforward approach to diagnosis and treatment more difficult and frustrating than myoclonus, due to its plethora of causes and its variable classifications. Nevertheless, in recent years, exciting advances have been made in the elucidation of the pathophysiology and genetic basis of many disorders presenting with myoclonus. Here, we provide a review of all of the important types of myoclonus encountered in pediatric and adult neurology, with an emphasis on the recent developments that have led to a deeper understanding of this intriguing phenomenon. An up-to-date list of the genetic basis of all major myoclonic disorders is presented. Randomized studies are scarce in myoclonus therapy, but helpful pragmatic approaches at diagnosis as well as treatment have been recently suggested.