Myoclonus in the critically ill: Diagnosis, management, and clinical impact

Abstract

Myoclonus is the second most common involuntary non-epileptic movement in intensive care units following tremor-like gestures. Although there are several types of myoclonus, they remain underappreciated, and their diagnostic and prognostic associations are largely ignored. This review discusses clinical, electrophysiological, neuroanatomical, and neuroimaging characteristics of different types of myoclonus in critically ill adults along with their prognostic impact and treatment options. Myoclonus is characterized by a sudden, brief, and sometimes repetitive muscle contraction of body parts, or a brief and sudden cessation of tonic muscle innervation followed by a rapid recovery of tonus. Myoclonus can resemble physiologic and other pathologic involuntary movements. Neurologic injuries, anesthetics, and muscle relaxants interfere with the typical appearance of myoclonus. Identifying "real myoclonus" and determining the neuroanatomical origin are important, as treatment responses depend on the involved neuroanatomical structures. The identification of the type of myoclonus, the involved neuroanatomical structures, and the associated illnesses is essential to direct treatment. In conclusion, the combined clinical, electrophysiological, and neuroradiological examination reliably uncovers the neuroanatomical sources and the pathophysiology of myoclonus. Recognizing cortical myoclonus is critical, as it is treatable and may progress to generalized convulsive seizures or status epilepticus.

Post-hypoxic myoclonus: Differentiating benign and malignant etiologies in diagnosis and prognosis

“…This distinction is key, because many cases previously described as “acute” PHM were later diagnosed as being LAS once the patient awakened (Freund et al, 2016, Gupta and Caviness, 2016). Specific clinical indicators that have been studied to discriminate LAS and MSE, and to delineate subtypes of MSE include: time to onset of myoclonus after CA (Bouwes et al, 2012, Gupta and Caviness, 2016, Malhotra and Mohinder, 2012, van Zijl et al, 2016), outcomes (Bouwes et al, 2012, Elmer et al, 2016, English et al, 2009, Harper and Wilkes, 1991, Lance and Adams, 1963, Malhotra and Mohinder, 2012, Rossetti et al, 2016, Seder et al, 2015, Sutter et al, 2016, Wijdicks et al, 1994, Young et al, 1990), response to treatment (Chadwick et al, 1977, Werhahn et al, 1997, Witte et al, 1988), clinical characteristics of myoclonus (Bouwes et al, 2012, English et al, 2009, Gupta and Caviness, 2016, Hallett et al, 1977, Hallett, 2000, van Zijl et al, 2016), and neurologic exam with particular focus on the presence of coma (English et al, 2009). …”

“…Given the appearance of epileptiform activity both clinically and electroencephalographically, anti-seizure drugs (ASD) are often first line, with anesthetics used if these fail (Gupta and Caviness, 2016). Clonazepam is often used, and serotoninergic medications have also been tried (Hallett, 2000) though myoclonus in MSE is usually difficult to treat (Sutter et al, 2016). Previously it was believed that the anatomic localization of myoclonus could be made based on the response to treatment, but has not been consistently demonstrated (Chadwick et al, 1977, Werhahn et al, 1997, Witte et al, 1988).…”

“…The mortality in patients with MSE after CA ranges from 90 to 100% (Bouwes et al, 2012, Elmer et al, 2016, Rossetti et al, 2016, Seder et al, 2015, Sutter et al, 2016, Wijdicks et al, 1994, Young et al, 1990). The chances of a good neurologic outcome in survivors is also low (Seder et al, 2015, Sutter et al, 2016).…”

“…“Acute” PHM (also referred to as myoclonus status epilepticus (MSE)) is the clinical appearance of nearly continuous myoclonic jerking for at least 30 min (Sandroni et al, 2015, Wijdicks et al, 2006). MSE was previously believed to indicate a poor prognosis (Wijdicks et al, 1994, Wijdicks et al, 2006, Young et al, 1990) but this is being challenged by increasing reports of cases with a favorable outcome (Freund et al, 2016, Gupta and Caviness, 2016, Lucas et al, 2012, Malhotra and Mohinder, 2012, Seder et al, 2015, Sutter et al, 2016). Conversely, “chronic” PHM or Lance-Adams syndrome (LAS) portends a better prognosis (Malhotra and Mohinder, 2012).…”

Myoclonus after Cardiac Arrest: Where Do We Go from Here?

“…Other studies around that time also confirmed a poor prognosis in those with early PHM (11,12). Though more recent studies have reaffirmed the 0% false positive rate in determining poor outcome due to myoclonus (13)(14)(15)(16)(17)(18)(19), there have been a number of publications that demonstrate a higher false positive rate (3)(4)(5)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32), and have since challenged the way we view early PHM (33).…”