How to Do an Electrophysiological Study of Myoclonus.

SUMMARY: Diagnosing and characterizing myoclonus can be challenging. Many authors agree on the need to complement the clinical findings with an electrophysiological study to characterize the movements. Besides helping to rule out other movements that may look like myoclonus, electrophysiology can help localize the source of the movement. This article aims to serve as a practical manual on how to do a myoclonus study. For this purpose, the authors combine their experience with available evidence. The authors provide detailed descriptions of recording poly-electromyography, combining electroencephalography and electromyography, Bereitschaftspotentials, somatosensory evoked potentials, and startle techniques. The authors discuss analysis considerations for these data and provide a simplified algorithm for their interpretation. Finally, the authors discuss some factors that they believe have hindered the broader use of these useful techniques.

Cortical mechanisms of sensory trick in cervical dystonia.

Patients with cervical dystonia (CD) often show an improvement in dystonic posture after sensory trick (ST), though the mechanisms underlying ST remain unclear. In this study, we aimed to investigate the effects of ST on cortical activity in patients with CD and to explore the contribution of motor and sensory components to ST mechanisms. To this purpose, we studied 15 CD patients with clinically effective ST, 17 without ST, and 14 healthy controls (HCs) who mimicked the ST. We used electroencephalographic (EEG) recordings and electromyography (EMG) data from bilateral sternocleidomastoid (SCM) muscles. We compared ST-related EEG spectral changes from sensorimotor and posterior parietal areas and EMG power changes between groups. To better understand the contribution of motor and sensory components to ST, we tested EEG and EMG correlates of three different conditions mimicking ST, the first without skin touch ("no touch" condition), the second without voluntary movements ("passive" condition), and finally without arm movements ("examiner touch" condition). Results showed ST-related alpha desynchronization in the sensorimotor cortex and theta desynchronization in the sensorimotor and posterior parietal cortex. Both spectral changes were more significant during maneuver execution in CD patients with ST than in CD patients without ST and HCs who mimicked the ST. Differently, the "no touch", "passive", or "examiner touch" conditions did not show significant differences in EEG or EMG changes determined by ST execution/mimicking between CD patients with or without ST. A higher desynchronization within alpha and theta bands in the sensorimotor and posterior parietal areas correlated with a more significant activity decrease in the contralateral SCM muscle, Findings from this study suggest that ST-related changes in the activity of sensorimotor and posterior parietal areas may restore dystonic posture and that both motor and sensory components contribute to the ST effect.

Diagnostic Neurophysiologic Biomarkers for Task-Specific Dystonia.

Background: Task-specific dystonia (TSD) is a challenging clinical diagnosis with no objective diagnostic biomarkers. Objective: The objective of this study was to test 2 neurophysiologic variables using transcranial magnetic stimulation as potential diagnostic biomarkers for TSD. Methods: We tested (1) cortical silent period (CSP) and (2) dorsal inferior parietal lobule-motor cortex (dIPL-M1) physiologic connectivity in 9 patients with the writer's cramp form of TSD and 12 healthy volunteers on 2 separate sessions. Results: CSP was significantly prolonged (P < 0.0001) in TSD and could classify TSD with high sensitivity and specificity with areas under the receiver operating characteristic curve (AUCs) = 0.94 and 0.90, respectively, for 2 separate sessions with an intraclass correlation = 0.79. dIPL-M1 interaction was notable for significant motor cortical inhibition in TSD compared with facilitation in healthy subjects (P < 0.0001) and could classify TSD with high sensitivity and specificity with AUCs = 0.96 and 0.86, respectively. Conclusion: CSP and dIPL-M1 physiologic connectivity can classify TSD with high sensitivity, specificity, reproducibility, and reliability.

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.

The role of the inferior parietal lobule in writer's cramp.

Humans have a distinguishing ability for fine motor control that is subserved by a highly evolved cortico-motor neuronal network. The acquisition of a particular motor skill involves a long series of practice movements, trial and error, adjustment and refinement. At the cortical level, this acquisition begins in the parieto-temporal sensory regions and is subsequently consolidated and stratified in the premotor-motor cortex. Task-specific dystonia can be viewed as a corruption or loss of motor control confined to a single motor skill. Using a multimodal experimental approach combining neuroimaging and non-invasive brain stimulation, we explored interactions between the principal nodes of the fine motor control network in patients with writer's cramp and healthy matched controls. Patients and healthy volunteers underwent clinical assessment, diffusion-weighted MRI for tractography, and functional MRI during a finger tapping task. Activation maps from the task-functional MRI scans were used for target selection and neuro-navigation of the transcranial magnetic stimulation. Single- and double-pulse TMS evaluation included measurement of the input-output recruitment curve, cortical silent period, and amplitude of the motor evoked potentials conditioned by cortico-cortical interactions between premotor ventral (PMv)-motor cortex (M1), anterior inferior parietal lobule (aIPL)-M1, and dorsal inferior parietal lobule (dIPL)-M1 before and after inducing a long term depression-like plastic change to dIPL node with continuous theta-burst transcranial magnetic stimulation in a randomized, sham-controlled design. Baseline dIPL-M1 and aIPL-M1 cortico-cortical interactions were facilitatory and inhibitory, respectively, in healthy volunteers, whereas the interactions were converse and significantly different in writer's cramp. Baseline PMv-M1 interactions were inhibitory and similar between the groups. The dIPL-PMv resting state functional connectivity was increased in patients compared to controls, but no differences in structural connectivity between the nodes were observed. Cortical silent period was significantly prolonged in writer's cramp. Making a long term depression-like plastic change to dIPL node transformed the aIPL-M1 interaction to inhibitory (similar to healthy volunteers) and cancelled the PMv-M1 inhibition only in the writer's cramp group. These findings suggest that the parietal multimodal sensory association region could have an aberrant downstream influence on the fine motor control network in writer's cramp, which could be artificially restored to its normal function.

Evidence already exists for motor system reorganization in CRPS.

Complex regional pain syndrome (CRPS) is a disabling condition that is usually preceded by trauma or surgical procedure. Involvement of the motor system is a well-known phenomenon in CRPS, though the pathophysiologic mechanisms of motor system affliction in CRPS are poorly understood. Graded motor imagery (GMI) has been proposed to be one of the therapeutic interventions to help improve pain and other disabling symptoms associated with CRPS, though the benefits noted are modest and inconsistent. The neurophysiological mechanisms implicated in motor imagery are intended to target the aberrant prefrontal and sensorimotor integration areas, which may potentially help restore the aberrant cortical plasticity in CRPS. Detailed well-controlled experiments using insights from the existing body of literature on motor system reorganization in CRPS are required to better understand this complicated disorder. Attempts to gain pathophysiologic insights about complicated disorders like CRPS based on case reports with poorly performed and uncontrolled interventions are misguided.

Le syndrome douleureux régional complexe est une affection invalidante habituellement précédée d'un traumatisme ou d'une intervention chirurgicale. L'implication du système moteur dans le SDRC est un phénomène bien connu, malgré le fait que les mécanismes pathophysiologiques qui l'affectent soient mal compris. L'imagerie motrice progressive (IMP) a été proposée en tant que l'une des interventions théraeutiques pouvant aider à améliorer la douleur et d'autres symptômes invalidants associés au SDRC, bien que les effets bénéfiques observés soient modestes et contradictoires. Les mécanismes neurophysiologiques impliqués dans l'imagerie motrice sont destinés à cibler l'aire préfrontale et l'aire d'intégration sensorimotrice anormales qui peuvent potentiellement aider à rétablir la plasticité corticale dans le SDRC. Des expériences approfondies bien contrôlées fondées sur les connaissances que l'on retrouve dans la littérature existante en ce qui concerne la réorganisation du système moteur dans le SDRC sont nécessaires afin de mieux comprendre ce trouble compliqué. Les tentatives pour améliorer les connaissances pathophsyiologiques concernant des troubles compliqués comme le SDRC qui sont fondées sur des études de cas et des interventions effectuées de manière médiocre et non contrôlées sont malavisées.

Cervical angina: an overlooked source of noncardiac chest pain.

Cervical angina has been widely reported as a cause of chest pain but remains underrecognized. This series demonstrates the varied clinical presentation of patients with cervical angina, the delay in diagnosis, and the extensive cardiac examinations patients with this condition typically undergo prior to a definitive diagnosis. Recognition of this condition in patients with acute chest pain requires a high index of suspicion and an awareness of the common presenting features and clinical findings of cervical angina.