Objective: To highlight the presentation of orthostatic myoclonus and to increase awareness of this syndrome amongst neurologists and physicians.

Background: Orthostatic unsteadiness (unsteadiness on standing) is a relatively common problem and can have neurological or non-neurological causes. Glass et al (Neurology, 2007) have recently described this syndrome which presents as unsteadiness during standing or jerking during upright posture or gait initiation difficulty. Orthostatic myoclonus (OM) a disabling syndrome but potentially treatable may develop on the background of neurodegenerative disease, other causes include pro-myoclonic drugs such as tricyclic antidepressants .

Methods: We report 4 cases of electrophysiologically confirmed orthostatic myoclonus who were referred to the movement disorder unit for lower limb nerve studies.

Results: All four patients presented with unsteadiness on standing. There were no signs suggestive of a neurodegenerative disease, three of the patients were thought to have orthostatic tremor. Diagnosis was supported by a surface electromyography showing (9-16 Hz) non-rhythmic muscle bursts with a burst duration of 50-100 milliseconds during standing.

Conclusions: The most common syndrome with which OM may be confused is orthostatic tremor. OM is unrecognized by many physicians as a cause of orthostatic intolerance. Surface EMG can be useful in differentiating orthostatic myoclonus from orthostatic tremor. A correct diagnosis is important as it may respond to treatment with clonazepam, gabapentin or piracetam.

Presented as a poster at the Australian New Zealand Association of Neurologist in 2014. However, with slight differences, the title then was (Orthostatic Myoclonus: A report of three cases).

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MDS Abstracts - https://www.mdsabstracts.org/abstract/ortostatic-myoclonus-a-report-of-four-cases/