58.: Orthostatic myoclonus: A report of three patients

Abstract

This report aims to highlight the presentation of orthostatic myoclonus and to increase awareness of this syndrome amongst neurologists and physicians. Orthostatic unsteadiness (unsteadiness on standing) is a relatively common problem and can have neurological or non-neurological causes. In 2007 Glass et al. 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 . We report patients with electrophysiologically confirmed orthostatic myoclonus who were referred to the movement disorder unit for lower limb nerve studies. All three patients presented with unsteadiness on standing. There were no signs suggestive of a neurodegenerative disease, and two 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 20–100 milliseconds during standing. 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 electromyogram 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.