Electrophysiological Investigations in Orthostatic Myoclonus: Preliminary Findings

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.

Myoclonus and other jerky movement disorders

Myoclonus and other jerky movements form a large heterogeneous group of disorders. Clinical neurophysiology studies can have an important contribution to support diagnosis but also to gain insight in the pathophysiology of different kind of jerks. This review focuses on myoclonus, tics, startle disorders, restless legs syndrome, and periodic leg movements during sleep. Myoclonus is defined as brief, shock-like movements, and subtypes can be classified based the anatomical origin. Both the clinical phenotype and the neurophysiological tests support this classification: cortical, cortical-subcortical, subcortical/non-segmental, segmental, peripheral, and functional jerks. The most important techniques used are polymyography and the combination of electromyography-electroencephalography focused on jerk-locked back-averaging, cortico-muscular coherence, and the Bereitschaftspotential. Clinically, the differential diagnosis of myoclonus includes tics, and this diagnosis is mainly based on the history with premonitory urges and the ability to suppress the tic. Electrophysiological tests are mainly applied in a research setting and include the Bereitschaftspotential, local field potentials, transcranial magnetic stimulation, and pre-pulse inhibition. Jerks due to a startling stimulus form the group of startle syndromes. This group includes disorders with an exaggerated startle reflex, such as hyperekplexia and stiff person syndrome, but also neuropsychiatric and stimulus-induced disorders. For these disorders polymyography combined with a startling stimulus can be useful to determine the pattern of muscle activation and thus the diagnosis. Assessment of symptoms in restless legs syndrome and periodic leg movements during sleep can be performed with different validated scoring criteria with the help of electromyography.

Orthostatic myoclonus - A retrospective study of Asian patients

BACKGROUND/PURPOSE

Orthostatic myoclonus (OM) is myoclonic jerks in both legs during standing. It may relate to gait unsteadiness and may be associated with various diagnoses, including neurodegenerative, systemic, and musculoskeletal diseases. Diagnosis is based on the surface electromyography (SEMG).

METHODS

From January 2016 to June 2020, we retrospectively reviewed 35 patients diagnosed with OM based on the SEMG criteria and analyzed the electrophysiological data.

RESULTS

The mean age was 75.3±8.9. Disease duration ranged from 2 days to several years. Genders were equally affected. The most common symptom was gait disturbance, and the next was leg tremulous sensation, followed by backward disequilibrium. 28.6% of our patients had falls. Electrophysiologically, bursting duration shorter than 100 ms supported the myoclonic origin from the cortex. The bursting activity occurred only on the upright and weight-bearing leg. The associated diagnoses included lumbosacral radiculopathy (28.6%), lumbosacral radiculopathy plus myasthenia gravis (2.9%), lumbosacral radiculopathy plus vascular parkinsonism (5.7%), diabetic polyneuropathy (5.7%), vascular parkinsonism (17.1%), Parkinson's disease (PD) (14.2%), normal pressure hydrocephalus (5.7%), medication-induced parkinsonism (2.9%), cervical myelopathy (2.9%), medication-related myoclonus (2.9%), and unknown (11.4%). In PD, OM was present before, along with, or after PD diagnosis. The myoclonic activity disrupted the parkinsonian tremor upon standing on SEMG.

CONCLUSION

OM is a syndrome instead of a diagnosis. It is more prevalent in the elderly with gait disturbance and patients will not necessarily fall. It is associated with central and peripheral nerve system disorders, systemic diseases, and medication use. We hypothesize that OM is a pathological disintegration of motor circuit.