Propriospinal myoclonus

Abstract

Objective: Propriospinal myoclonus (PSM) is a rare disorder with repetitive, usually flexor arrhythmic brief jerks of the trunk, hips, and knees in a fixed pattern. It has a presumed generation in the spinal cord and diagnosis depends on characteristic features at polymyography. Recently, a historical paradigm shift took place as PSM has been reported to be a functional (or psychogenic) movement disorder (FMD) in most patients. This review aims to characterize the clinical features, etiology, electrophysiologic features, and treatment outcomes of PSM.Methods: Re-evaluation of all published PSM cases and systematic scoring of clinical and electrophysiologic characteristics in all published cases since 1991.Results: Of the 179 identified patients with PSM (55% male), the mean age at onset was 43 years (range 6-88 years). FMD was diagnosed in 104 (58%) cases. In 12 cases (26% of reported secondary cases, 7% of total cases), a structural spinal cord lesion was found. Clonazepam and botulinum toxin may be effective in reducing jerks.Conclusions: FMD is more frequent than previously assumed. Structural lesions reported to underlie PSM are scarce. Based on our clinical experience and the reviewed literature, we recommend polymyography to assess recruitment variability combined with a Bereitschaftspotential recording in all cases. Propriospinal myoclonus (PSM) is a rare hyperkinetic movement disorder involving the axial muscles.1 Brown et al. 1 were the first to describe the clinical phenomenology based on 3 cases. PSM is characterized by painless, usually flexor arrhythmic jerks of the trunk, hips, and knees, which are often stimulus sensitive and typically increase when supine.1-3 Based on the initial publications, PSM had a presumed generation in the spinal cord and diagnosis depended on characteristic features at polymyography. [1][2][3][4] The myoclonic activity in PSM was assumed to originate from a spinal generator and spread up and down the spinal cord via intrinsic propriospinal pathways, and these axial jerks were therefore termed propriospinal myoclonus.1 Electrophysiologic features of PSM were published after the first clinical descriptions and included a fixed pattern of muscle activation, a slow conduction velocity (5-15 m/s) consistent with spread within the propriospinal tract, EMG burst duration of less than 1,000 ms, synchronous activation of agonist and antagonist muscles, and no facial involvement. 4 Until recently, patients were subdivided into idiopathic PSM (i.e., primary, no underlying cause found) and secondary PSM. However, the diverse etiology of this disorder is currently highlighted by several movement disorders specialists, including our centres.5-7 A functional etiology was reported to underlie several PSM cases. Psychogenic or functional movement disorders (FMD) are common and characterized by abnormal movements inconsistent with a known organic etiology. 8

Functional movement disorders

“…Axial jerks are more likely to represent functional jerks (58% of propriospinal myoclonus) [38,39]. Arguments in favor of functional propriospinal myoclonus are [1] previous somatizations, [2] coexistence of facial involvement (do not occur with a spinal origin), [3] normal imaging of the spinal axis [4], and presence of Bereitschaftspotential (cave: latter can be absent or not recordable) or inconsistent electromyogram pattern [39][40][41].…”

“…Tics are usually experienced as intentional movements performed in order to relieve inner tension, whereas functional tics are perceived as involuntary [51,52]. Premonitory sensation is considered a hallmark feature of organic tics, and it is reported in about 90% of patient (although also reported in patients with presumed functional tics) [39,52], but larger studies are needed [49,51] to have definite views on this issue. (Table 1) …”

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

“…With propriospinal myoclonus, many patients have psychogenic myoclonus calling for psychiatric intervention (van der Salm et al, 2014) together with clonazepam as the first-line drug for segmental and propriospinal myoclonus. Alternatively, zonisamide can be effective for propriospinal myoclonus (Dijk and Tijssen, 2010).…”

Sleep‐related motor and behavioral disorders: Recent advances and new entities

“…However, it was subsequently found that the EMG pattern of propriospinal myoclonus could be mimicked voluntarily by healthy individuals, 104 and now a significant proportion of patients are believed to have a functional etiology. 105 It is completely unknown whether propriospinal myoclonus at sleep onset has the same underlying etiology as in those patients experiencing daytime propriospinal myoclonus. Clonazepam and levetiracetam have been used successfully to reduce the number of myoclonic events and improve sleep efficiency.…”