Imported: 2024-12-31
“Myoclonus is a hyperkinetic movement disorder typically characterized by sudden brief, jerk-like movements(1). Several movement disorders such as tics, chorea, ballism, functional jerks, and dystonia can have ‘jerk-like’ phenomenology. High frequency repetitive myoclonic jerks can also be misclassified as tremors.” Yellow Highlight Page
Myoclonus definition, examples, and misclassifications
“Suggested filter settings for EMG recordings are 20-300 Hz that will capture most EMG frequency content; therefore, a sampling frequency of at least 1 KHz is needed (7). As the recorded movements are brisk, artifacts can be a problem.” Yellow Highlight Page 2
EMG filtration and sampling frequencies
“For cranial or upper limb involvement, we place contralateral central and frontal leads (e.g., C3 and F3 for right-side movement) and reference to the contralateral mastoid. For lower limbs Cz and Fz can be used. Conventional EEG filtering parameters can be used.” Yellow Highlight Page 3
EMG referencing for different movements and conventional filtering parameters
“BP is a very long potential which can be captured by placing one EEG electrode on the contralateral sensorimotor area while simultaneously recording EMG from the active muscle or muscle groups.” Yellow Highlight Page 3
Singular EEG electrode for BP recording
“For this reason, a high-pass filter of 0.1 Hz (or even DC) should be used (we use 0.01 Hz in our lab).” Yellow Highlight Page 3
0.01 Hz high pass filter for BP
“Cortical myoclonus is a manifestation of cortical hyperexcitability. Enhanced SEP and C reflexes are physiologic correlates of cortical hyperexcitability and associated enhancement of long-loop reflexes.” Yellow Highlight Page 4
Study for cortical hyperexcitability using SEP and C reflexes
“Quantifying the length of the muscle bursts provides an idea of the movemenťs source. Voluntary or functional movements usually have a duration higher than 100ms. Myoclonus coming from the spine can also have durations longer than 200ms. Cortical myoclonus almost always has a duration lower than 50ms. Subcortical myoclonus can be in the range of 50-100ms, but also shorter durations similar to cortical myoclonus(18). An example can be seen in Figure 2. It is also important to look for silences in the ongoing EMG that may demonstrate negative myoclonus.” Yellow Highlight Page 5
EMG burst duration for classifying movements, and silences as possible signs of negative myoclonis
“The temporal and spatial characteristics of the pattern of muscle activation is also very helpful. The coactivation of agonist and antagonists is typical of central origin and can help differentiate short duration myoclonus (20ms) from a fasciculation that can look very similar. The temporal pattern of spread of muscle activation can also help with localization of the origin of the ‘jerk-like’ movement within the neuroaxis. The startle reflex, which originates in the nucleus reticularis pontis caudalis, has a clear rostro-caudal progression of the EMG activity through the cranial nerves. On the other hand, an inconsistent order of muscle activation which is variable with each movement, will point to a functional syndrome.” Yellow Highlight Page 5
Pattern of EMG activations can provide insight into the origin of the movements
“For myoclonus of cortical origin, the fact that the time between the cortical activation and the muscle activation is fixed, by averaging several segments with the EMG burst the EEG that is time-locked to the EMG activity will remain and the activity that is not time-locked will cancel out.” Yellow Highlight Page 6
Back averaging for myoclonus of cortical origin
“For the purpose of this educational review, we will focus on 2 main issues: (1) limited training available for performing these techniques, and (2) lack of specialized/ standardized equipment and software.” Yellow Highlight Page 7
2 main issues for electrophysiology