Adult-Onset Myoclonus: Comparisons and Contrasts in the Inpatient and Outpatient Settings

Background: Myoclonus is a hyperkinetic movement disorder presenting as rapid jerky involuntary movements. The etiology of myoclonus differs between in-hospital and outpatient clinic settings. Historically, those in the hospital typically develop myoclonus from toxic-metabolic or hypoxic-ischemic etiologies, whereas those presenting to a clinic tend to have an underlying neurodegenerative etiology.

Methods: We retrospectively reviewed charts of both inpatient and outpatient adult cases with myoclonus at New York Presbyterian Brooklyn Methodist Hospital over 10 years. Data were analyzed with descriptive statistical methods to elucidate demographics, etiologies, and outcomes.

Results: Overall, 279 inpatient (56.63% female aged 70.61 + 15.76 years) and 85 outpatient (52.9% female aged 64.3 + 16.3 years) individuals were included in our study. Outpatient cases were younger on average than inpatient counterparts (p < 0.05). While more Caucasian individuals were seen in the outpatient setting, more black individuals were seen in the inpatient setting; ethnic distributions did not differ significantly between the two cohorts (p > 0.05). Longer symptom duration was prevalent in outpatient cases (IQR 3–45 months) compared to inpatient (IQR < 1–4 days) ones (p < 0.05). Etiological distributions varied between the two cohorts, with toxic/drug-induced, metabolic (non-genetic), and static hypoxic/ischemic etiologies predominating our inpatient cohort, and neurodegenerative, inflammatory/autoimmune/paraneoplastic, and idiopathic etiologies more prevalent in the outpatient setting. Spinal nervous system lesion and toxic/drug-induced outpatient cases tended to present focally, but inflammatory/autoimmune/paraneoplastic etiologies were associated with axial-predominant symptoms among our outpatient cohort (p < 0.05). Responses to treatment of underlying etiology and/or anti-seizure drugs was robust in both settings overall, with over 70% of individual cases showing response.

Conclusions: Myoclonus in the inpatient and outpatient settings have differences in etiology and symptom duration, with longer duration and more neurodegenerative and inflammatory/autoimmune/paraneoplastic etiologies predominating in the outpatient cohort compared to the inpatient one. List of causes of myoclonus do not typically differentiate between the presentation in inpatient and outpatient settings. If the causes differ by setting, listing causes by setting may aid clinicians in ranking a priori probabilities.