Adult-Onset Myoclonus in a Large Urban Inpatient Setting: A Retrospective Cohort Study

Background: Myoclonus is a hyperkinetic movement with various attributable etiologies, semiologies, and treatment outcomes. To our knowledge, few studies investigated adult-onset myoclonus in an inpatient setting.

Methods: We retrospectively reviewed charts of adult inpatients with myoclonus at New York Presbyterian Brooklyn Methodist Hospital between 2011 and 2021. Data was analyzed with descriptive statistical methods to elucidate etiology-specific demographics and outcomes.

Results: 279 individuals, 56.63% female, were included in our study, aging at 70.61 + 15.76 years. More than 50% were not initially diagnosed with myoclonus by the admitting medical team, and more than 50% had 2 or more ascribable etiologies. Symptomatic myoclonus – mostly of toxic-metabolic or hypoxic-ischemic etiology – accounted for most cases. Hypoxic-ischemic etiologies had shorter durations prior to presentation and were also most resistant to treatment. Renal-associated myoclonus was most associated with asterixis, whereas stimulus-sensitive myoclonus was strongly associated with hypoxic-ischemic etiology. Mortality in-hospital was strongly associated with hypoxic-ischemic etiology and least associated with neurodegenerative and idiopathic etiologies. Treatment response rate diminished in patients who were tried on a second or third anti-seizure drug compared to those trialed on one.

Discussion: Myoclonus remains an underdiagnosed hyperkinetic movement disorder with various ascribable etiologies of varying demographic characteristics and treatment outcomes.