Sleep Medicine Reviews xxx (2014) 1e10

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CLINICAL REVIEW

Propriospinal myoclonus: The spectrum of clinical and neurophysiological phenotypes Elena Antelmi a, b, Federica Provini a, c, * a

Department of Biomedical and Neuromotor Sciences, Alma Mater Studiorum, University of Bologna, Bologna, Italy Department of Medical and Surgical Sciences, DIMEC, University of Bologna, Bologna, Italy c IRCCS Institute of Neurological Sciences, Bologna, Italy b

a r t i c l e i n f o

s u m m a r y

Article history: Received 17 June 2014 Received in revised form 23 October 2014 Accepted 24 October 2014 Available online xxx

Propriospinal myoclonus (PSM) is a rare type of spinal myoclonus characterized by muscle jerks that usually start in the midthoracic segments and then slowly propagate up and down into the spinal cord, resulting in repetitive and irregular jerky flexion, or extension of the trunk, neck, knees and hips. PSM can be symptomatic, but up to 80% of reported cases appear idiopathic. PSM tends to occur especially while the subject is lying down. PSM at sleep onset was first described by experts in sleep medicine. The original electrophysiological features included fixed pattern of muscle activations, slow spinal cord conduction (5e15 m/s), electromyographic burst duration less than 1000 ms, synchronous activation of agonist and antagonist muscles and no involvement of facial muscles. PSM has been reported to be a functional (psychogenic) movement disorder in a number of cohorts. The differential diagnosis between idiopathic PSM and the functional forms is not always straightforward. A consistent polymyographically documented muscle activation pattern may be supportive but by no means sufficient and additional neurophysiological investigations are required. PSM should be differentiated from other movement disorders involving the abdomen and trunk, or occurring at sleepewake transition. This article offers a comprehensive overview of the spectrum of PSM phenotypes. © 2014 Elsevier Ltd. All rights reserved.

Keywords: Propriospinal myoclonus Spinal myoclonus Axial myoclonus Sleep-related movement disorder Pre-dormitum

Introduction Propriospinal myoclonus (PSM) is a rare hyperkinetic movement disorder, first described by Brown and colleagues in 1991 [1]. It is a type of spinal myoclonus (SM) with a peculiar slow propagation up and down the spinal cord, provoking repetitive and arrhythmic jerky flexion, or less frequently extension of the trunk and sometimes of the neck, knees and hips [1,2]. PSM can appear in any body position and at any moment of the day but frequently worsens when patients sit or lie flat. Still, as documented in patients refered to sleep specialists [3,4], PSM can appear especially during relaxed wakefulness preceding sleep onset. The neurophysiological pattern of PSM suggests that the disorder arises from a spinal generator, most commonly at the thoracic level [1,2].

* Corresponding author. Department of Biomedical and Neuromotor Sciences, University of Bologna, IRCCS Institute of Neurological Sciences, Bellaria Hospital, Via Altura, 3, 40139 Bologna, Italy. Tel.: þ39 051 4966829. E-mail address: [email protected] (F. Provini).

Papers on PSM have been published by experts in the fields of either movement disorders or sleep medicine, engendering a list of overlapping and sometimes undefined data. The first description of a spinal-generated myoclonus was confined to muscles innervated by a few adjacent spinal segments and reported as a rhythmic movement persisting in sleep [5] due to various local pathologies. Although, an experimental model of propriospinally-mediated myoclonus already exists in the cat [6] and a similar pattern may be recognized in previous case-reports [7,8], it was only in 1991 that Brown and colleagues reported such movement under the name of PSM [1]. Some years after Brown et al.'s first description [1], Montagna and colleagues [3] reported three cases in which PSM appeared only during relaxed wakefulness preceding sleep and at the sleepewake transition (namely stage 1 of non-rapid eye movement (NREM) sleep). In all three patients, the jerks were so bothersome as to preclude sleep onset, causing severe insomnia. Finally, a striking shift came with the first description of a case of functional (psychogenic) PSM [9] and with the paper by Kang and Shon [10] reporting that the typical pattern of PSM may be mimicked voluntary by healthy volunteers. After that, a number of cohorts with functional PSM

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Please cite this article in press as: Antelmi E, Provini F, Propriospinal myoclonus: The spectrum of clinical and neurophysiological phenotypes, Sleep Medicine Reviews (2014), http://dx.doi.org/10.1016/j.smrv.2014.10.007

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Abbreviations BP DD DTI EEG EMG EOG FT IHJ MRI PLMs PLMS PLMW PSG PSM RA RLS SCM SM SSM

Bereitschaftspotential differential diagnosis diffusion tensor imaging electroencephalography electromyography electro-oculography fiber tracking intensified hypnic jerks magnetic resonance imaging periodic limb movements periodic limb movements during sleep periodic limb movements during wakefulness polysomnography propriospinal myoclonus rectus abdominis restless legs syndrome sternocleidomastoideus spinal myoclonus spinal segmental myoclonus

have been described and so far, more than 50% of all the reported cases of PSM appear to be functional [11e15]. Hence, our current knowledge of PSM presents heterogeneous features that are difficult to disentangle. Three types of PSM have been reported to date: symptomatic, idiopathic and functional PSM. In addition, a peculiar subtype, mainly reported to be idiopathic, may be recognized because of its onset at the sleepewake transition [3,4]. However, the literature on PSM remains complex and confusing. Although neurophysiological recordings are reported in up to 90% of cases, few studies have conducted extensive electroencephalography (EEG)/electromyography (EMG) recordings with jerk locked back-averaging searching for pre-movement potentials (i.e., Bereitschaftspotential e BP) and seldom without standardized measurements. Hence, possible cases of functional PSM may have been included in the idiopathic cohort, yielding incorrect information. This article is a comprehensive overview of the clinical and neurophysiological data characterizing the spectrum of PMS phenotypes: symptomatic, idiopathic, functional and at sleep onset. It is aimed at clinicians faced with this peculiar disorder, to help them distinguish the different types of presentation and identify prominent features that may serve as diagnostic clues. The review will mainly focus on the different “forms” of PSM reported so far. Therapeutic options and differential diagnosis among other types of movement disorders involving axial muscles and appearing at sleep onset are also discussed. Search strategy and selection criteria References for the review were identified by searches of Pubmed between 1991 (year of the first formal report on PSM) and August 2014 using the search terms: spinal myoclonus, propriospin*, propriospinal myoclonus, propriospinal myoclonus at sleep onset and axial myoclonus. The search retrieved 49 papers on PSM. Reference lists of the articles were also checked for other relevant reports not indexed in the electronic database. Cases mentioned in more than one publication were only considered once. Given the paucity of literature on the matter, we decided to include all the articles including the two articles written in French and those in

which myoclonus polygraphic recordings were not available. In addition, original papers of interest reporting on related matter were included even if published before 1991. The PSM spectrum Clinical features PSM is a special type of spinal myoclonus characterized by brief, repetitive, mainly arrhythmic jerks. The jerks usually arise in the muscles corresponding to a given thoracic myelomere and then progressively and synchronously spread in rostral and caudal directions to the adjacent myotome at low velocity along propriospinal pathways [1e4,16]. The jerks usually provoke a flexion movement, but less frequently an extension pattern has been reported [16e19]. PSM most often seems to affect middle-aged men. There is only one description of a possible PSM in a child, after a back injury [19]. In around 80% of cases, PSM appears to be idiopathic, the remainder comprising patients with a broad range of medical conditions, including spinal lesions, namely cervical hemangioblastoma or cervical herniations, syringomyelia and dural arteriovenous fistula [1,20,21], paraneoplastic condition [18], paraproteinemic neuropathy [22], demyelinating lesions [23,24], thoracic herpes zoster [2], HIV infection [25], Lyme neuroborreliosis [26], fragile X permutation [27], celiac disease [28] and as a possible complication of an enteropathogenic toxin [29]. Different pharmacological treatments have also been associated with PSM onset, i.e., interferon-alpha [30], intrathecal bupivacaine [31,32], ciprofloxacin [33] and cannabis [34]. Although a clear lesion has been found on spinal magnetic resonance imaging (MRI) in some cases [1,16,17,20,23,24,35e38], the causal link remains speculative in many patients. Even among the cases with a clear spinal lesion, a clear correspondence between the spinal generator level and the level of the abnormalities detected by neuroimaging has only been reported in two cases [20,23]. Symptomatic PSM forms seem to be more prevalent among women. PSM usually arises in the thoraco-abdominal/paraspinal muscles (Figs. 1a and 2) or less frequently in cervical muscles such as the sternocleidomastoideus (SCM). Cranial muscles are usually not involved, even though a few electromyographic recordings have shown a slight activation of the masseter [22,27,36,39]. Sometimes the jerks remain localized in the single segmental muscle where the propagation usually starts [3,4,35]. Thus, focal-segmental axial myoclonus and PSM may coexist, suggesting that under conditions of heightened excitability, the same spinal generator responsible for a monomeric segmental myoclonus may cause a multimeric propriospinally propagated muscular activation. Various sensory warnings have been reported preceding the jerks [12,37], mainly strange sensations (such as tingling at the back of the neck, a shock-like internal sensation, a clicking sensation in the head, an inner sensation of electric shocks in the head or chest, a sensation of groin pressure and tingling from penis to trunk, and uncomfortable electrical current-like sensation) without a clear topography. Moreover, PSM may be stimulus-sensitive and evoked by somesthetic stimulation such as tapping of bicep or patellar tendons, but not usually by startle [4]. The movement seems to be position-dependent, recurring more frequently when the patient is lying down [1,16,22,24,28,31,35,40] and disappearing or subsiding when standing or walking. However, many of these reports did not check the data with the subject's state of mental activation. A few individual cases have been reported in which the movement seemed to be elicited by standing or changing position [27,30,41,42].

Please cite this article in press as: Antelmi E, Provini F, Propriospinal myoclonus: The spectrum of clinical and neurophysiological phenotypes, Sleep Medicine Reviews (2014), http://dx.doi.org/10.1016/j.smrv.2014.10.007

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Fig. 1. Propriospinal myoclonus at sleep onset. a. EMG recording of propriospinal myoclonus shows simultaneous spreading of jerks both rostrally and caudally. The onset of the EMG activity is in the right rectus abdominis (Rect Abd) muscle with later ordered involvement of muscles located rostrally and caudally: i.e., paraspinales (Parasp), biceps brachii (Bic Br), pectoralis (Pect), SCM, triceps brachii (Tric Br), rectus femoris (Rect Fem), gastrocnemius (Gastr). The propagation velocity is 2e16 m/s, b. Axial jerks recur in quasi-periodic sequences during the wakeesleep transition when alpha activity spreads to the anterior EEG regions, c. Polysomnographic study shows the jerks recurring for many hours before sleep onset and disappearing during sleep. When the patient was mentally activated during wakefulness before sleep onset (bold line) the jerks disappeared even if the patient remained lying down in the same body position. EMG: Electromyography, SCM: sternocleidomastoideus, EEG: electroencephalography.

Some patients report an “urge to perform” the jerks suggesting similarities with a tic disorder, as already pointed out [12]. Additionally, patients can sometimes suppress the movements on volition, even if usually only for few seconds. Finally, several functional cases-series have been reported, mainly from the Netherlands [12] and the UK [11,14,15]. According to the former, criteria suggesting a functional origin include: 1) acute onset of the disorder; 2) rapid progression of symptoms after onset, and spontaneous (albeit temporary) remissions; 3) previous somatizations; 4) non-objectifiable (neurological) complaints and psychiatric co-morbidity; 5) distractibility, variability (over time) and inconsistency (at time of visit) in the jerks; 6) involvement of facial or neck muscles [12]. Still, the absence of a stereotyped pattern of jerks with onset in the same patient and at different times from different muscles and an immediate response to botulinum toxin injection [14], may represent further clues suggesting a functional origin of the jerks. However, acute onset of PSM may also be ascribed to the occurrence of an acute spinal lesion and even the criterion of distractibility does not seem very useful. Thus, if the cessation of jerks may be seen as a proof of distractibility by a movement disorders expert, it may instead be a marker of a different state of brain activity if seen by a sleep expert and cessation due to arithmetic tasks has been reported in PSM at sleep onset [3,4]. Instead, premonitory sensations, urge, relief and the ability to suppress the jerks and rebound after suppression were considered suggestive of a tic disorder [12].

PSM at sleep onset PSM worsening at sleep onset was first reported by sleep medicine experts [3,4,22,24,35,39], but also in other case-reports and cohort studies [19,28,36,37,43,44]. Indeed, it seems to be a peculiar feature of PSM even if it is not always reported, probably because clinicians do not always ask specifically about this feature [37]. Reports by sleep medicine experts cannot ascribe the typical window of occurrence to recumbence alone as polysomnographic (PSG) recordings showed that the onset of PSM coincided with the diffusion of EEG alpha activity to frontal areas. As soon as the N2 stage of NREM sleep proper set in and the EEG changed to spindles and k-complexes, PSM ceased (Fig. 1b and c). This typical pattern of occurrence emphasizes that the transition from wake to sleep represents a stage with independent neurophysiological, neuropsychological, neuroradiological and clinical characteristics. This had already been noted by Critchley who named this state of being as the pre-dormitum (1955) defining it as “a transition, sometimes gradual, sometimes abrupt, leads from a state of healthy alertness (wake) to one of unconsciousness (sleep)” [45]. Hence, the sleepewake transition, although usually defined as relaxed wakefulness and scored according to standard criteria as stage 1 NREM sleep, represents a peculiar unique state between active wakefulness and sleep proper [46,47], marking a physiological state dissociation and reflecting the neural local intrinsic properties of generating sleep and the time-related involvement of different corticothalamic structures [48,49].

Please cite this article in press as: Antelmi E, Provini F, Propriospinal myoclonus: The spectrum of clinical and neurophysiological phenotypes, Sleep Medicine Reviews (2014), http://dx.doi.org/10.1016/j.smrv.2014.10.007

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Fig. 2. EEGeEMG recording of propriospinal myoclonus at sleep onset. a: PSG recordings of a spontaneous single PSM jerk during relaxed wakefulness preceding sleep onset (note the slow eye movements on EOG traces), b. The EMG activity arises in the left rectus abdominis (Rect Abd) muscles with later ordered slow involvement of intercostalis (Interc), paraspinales (Parasp), rectus femoris (Rec Fem), tibialis anterior (Tib), flexor (Flex) and extensor (Ext) carpi, deltoideus (Delt) and SCM (dotted line). The propagation velocity is 4e5 m/s, c. During arousal from sleep myoclonic activity appears again but remains confined to the rectus abdominis muscles. EEG: electroencephalography, EMG: electromyography, EOG: electro-oculography, PSM: propriospinal myoclonus, SCM: sternocleidomastoideus.

Due to its independent clinical, neuropsychological and neurometabolic characteristics [50], this state seems to act as a pacemaker for many movement disorders besides PSM, i.e., rhythmic body movements, hypnic jerks and restless legs syndrome (RLS). Studies with full night video-PSG recordings showed that PSM appears only at sleepewake transition (stage 1 of NREM sleep), while it quickly disappears with stage 2 of NREM sleep onset [4,19,22,24,43,44]. A few studies have documented the persistence of the jerks during sleep [1,31,35,40], However, it is still not clear which underlying factor allows the jerks to persist during sleep. It could be hypothesized that sometimes the jerks appear only during an arousal from sleep (albeit not detectable on the scalp EEG). Indeed, we observed persistent movement during the night in one of our patients with idiopathic PSM. The movement appeared during EEG arousals from stage 1 and 2 of NREM sleep and remained segmental, i.e., restricted to the muscle from which the contraction originated (Fig. 2c). PSM has also been described in association with RLS [39]. Remarkably, in those patients PSM appeared only during relaxed wakefulness, and coexisted with motor restlessness and sensory discomfort in the limbs, typical of RLS. PSM, however, characteristically disappeared when spindles and K complexes appeared on the EEG and, at this time, typical periodic limb movements (PLMs) appeared. PSM at sleep onset was previously classified by the revised International Classification of Sleep Disorders (ICSD-2) [51] among the

“isolated symptoms, apparently normal variants and unresolved issues”, i.e., a section dedicated to sleep-related symptoms that either lie at the borderline between normal and abnormal sleep or that exist on the continuum of normal to abnormal events in sleep or conditions with insufficient information to include them as definitive pathologies. However, the new classification (ICSD-3) [52] has placed PSM at sleep onset among the “sleep-related movement disorders” being rarely associated with spinal cord lesions [24,35e37]. The ICSD-3 diagnostic criteria are the following: A) the patient complains of sudden jerks, mainly of the abdomen, trunk, and neck; B) the jerks appear during relaxed wakefulness and drowsiness, as the patient attempts to fall asleep; C) the jerks disappear upon mental activation and with onset of a stable sleep stage; D) the jerks result in difficulty initiating sleep; E) the disorder is not better explained by another sleep disorder, medical or neurological disorder, mental disorder, and medication use or substance use disorder [52]. Etiopathogenesis Since the original description, the pattern and velocity of PSM have been ascribed to a propriospinal volley. The propriospinal system has been described at C3eC4 spine level in the cat [53] and same data have been provided for the existence of a similar thoracic system in humans [54,55], even if evidence is still lacking. In many cases, the myoclonic generator was reported at the thoracic level,

Please cite this article in press as: Antelmi E, Provini F, Propriospinal myoclonus: The spectrum of clinical and neurophysiological phenotypes, Sleep Medicine Reviews (2014), http://dx.doi.org/10.1016/j.smrv.2014.10.007

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although the “primum movens” releasing this “quiescent generator” is unclear. In the first reports [1,16], intrinsic spinal cord lesions have been implicated in the partial release of a spinal motor generator by disrupting afferent signals originating distal to propriospinal pathways [56]. However, since most patients with PSM have a normal spinal cord on standard spinal MRI sequences, another possibility is that local hyperexcitability of the myoclonus generator is related to functional impairment or to abnormalities undetectable with conventional MRI [36,37]. The persistence and worsening of PSM during wakeesleep transition may be explained by the loss of supraspinal control over the spinal generator preceding sleep onset. Conceivably, reduced sleep-related spinal inhibition has been reported to result in activation of different motor generators, resulting in different types of movement disorders at sleepewake transition [57]. Propriospinal projections producing different responses in static versus locomotive situations probably could explain why PSM is typically more prominent in the supine position [58]. Ayache and colleagues [59] studied three patients with idiopathic PSM, analyzing the recruitment pattern of long-latency electromyographic reflexes in abdominal muscles. Such reflexes represent the electrical activity recordable on abdominal muscles in response to various stimuli, namely magnetic or electrical stimulation at different levels. They are linked to the spinal generator and controlled by supraspinal influences [60]. In the cohort of Ayache et al., [59] the evoked stereotyped long-latency abdominal reflexes showed the same features (spreading and duration) as the spontaneous PSM recorded in the same patients. These results point to the possible involvement of brain-stem structures (possibly the reticular formation) able to excite the spinal generator. Indeed, the reticular formation is known to produce extensive excitation of propriospinal neurons, which could in turn activate the thoracic spine generator, where increased excitability may lie. In this regard, such abdominal reflex responses could not have been produced in normal subjects, given the nature of the stimulation applied (namely painless sensory stimuli of low intensity). It remains to be determined whether these reflexes could help distinguish organically induced PSM from functional or mimicked PSM. Moreover, given the very long latency of these reflexes, it cannot be excluded that they represent a behavioral reaction, rather than a true reflex, as reported in the late component of the startle reflex [60]. Neurophysiological features PSM consists in single but more frequently repetitive, arrhythmic jerks of variable duration usually lasting between 100 and 1000 ms for each single jerk [1,3,4,16]. The first jerk will usually be recorded in axial muscles (mainly superior rectus abdominis (RA), then intercostalis, paraspinalis, sternocleidomastoideus (SCM)) or, more rarely arm muscles (biceps brachialis), later involving more cranial and more caudal muscles. Thus, the pattern of recruitment of electromyographic bursts will initially involve the midthoracic segments (myoclonic generator) followed by simultaneous and progressive propagation up and down the spinal cord via slowly conducting (average: 3e11 m/s) pathways, suggesting a polysynaptic transmission in the ventrolateral funiculus. The intermuscle latencies (first-to-last activated muscle) are usually about 16e200 ms, variable from one jerk to the other (Fig. 3; Table 1) [1,3,4,16]. The inconsistency of the muscle activation pattern may be a supportive [14] but by no means a diagnostic feature of functional spinal myoclonus [11]. An additional means of distinguishing idiopathic and functional jerks is the detection of a BP via EMG jerk-

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locked back-averaging analysis (Table 1) [11,12]. BP consists in a negative electrical shift over the central cortical areas that increases over time with amplitudes of at least 5 mV. It is recorded before selfpaced voluntary movements and has never been documented to occur in any type of proven organic movement disorder [61]. Thus, when EMG recording is coupled with EEG, no EEG activity preceding the jerks should be obtained upon back-averaging triggered on the EMG of the originating muscle. Reviewing all the cases of symptomatic PSM (# 32 cases), it emerges that BP has been searched in 68% cases and resulted negative in all of them. Hence, BP appeares a specific marker to exclude a frontal origin of the jerks, although many studies failed to report the criteria used to evaluate BP. In fact, no established criteria for existed until the recent paper by Van der Sam et al. (2012) [62]. Interestingly, in this paper the authors evaluated BP in a large case series of clinically established functional jerks, Gilles de la Tourette syndrome and myoclonus, concluding that the presence of the BP prior to psychogenic jerks had a sensitivity and specificity of 0.86. Not all functional movements disclose a BP and the absence of BP may reflect some technical limitations, such as bias when the jerks are too frequent or too sporadic, and artifacts due to head movements. Nonetheless, BP can be affected by the level of intention, motivation and attention. Indeed, BP cannot be found in 50% of cases classified to be functional PSM [11,12,14], thus its absence does not rule out a cortical origin. PSM may be stimulus-sensitive. It is commonly admitted that latency from stimulus to jerk above 100 ms may be suggestive of functional jerks. However, long latency (range 60e150 ms) responses to various stimuli have been reported in patients with PSM, including patients with obvious conventional spinal MRI abnormalities, such as syringomyelia, arteriovenous fistula, and demyelinating lesions [20,21,23].

Other instrumental examinations Spinal MRI may reveal spinal abnormalities in the symptomatic form of PSM (Table 1) and hence should always be performed even in the absence of clear abnormalities at neurological examination or at neurophysiological investigations, namely somatosensory evoked potentials or motor evoked potentials. By performing MRI diffusion tensor imaging (DTI) and fiber tracking (FT) in a cohort of patients with idiopathic PSM, Rose et al. [36,37] found thinning and disorganization of the spinal cord, arguing that a functional/structural impairment of the cord may be the cause of such a movement. However, it is still unclear whether these abnormalities are directly linked to the symptoms or whether they reflect a process associated with the primary dysfunction. In addition, DTI does not show abnormalities in all patients [37,59]. Thus, the sensitivity of DTI-FT analysis to support the diagnosis of organic PSM awaits further analysis and needs to be confirmed in larger controlled studies. Table 1 summarizes the main clinical and neurophysiological features of sleep-onset, symptomatic and functional PSM.

Differential diagnosis (DD) PSM should be differentiated from other movement disorders involving axial muscles such as spinal segmental myoclonus, belly dance dyskinesia, axial torsion dystonia and tics. PSM at sleeponset should be distinguished from those disorders typically occurring at sleep onset, such as intensified hypnic jerks and periodic limb movements during wakefulness.

Please cite this article in press as: Antelmi E, Provini F, Propriospinal myoclonus: The spectrum of clinical and neurophysiological phenotypes, Sleep Medicine Reviews (2014), http://dx.doi.org/10.1016/j.smrv.2014.10.007

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Fig. 3. EMG recording of propriospinal myoclonus. The recording shows a slow rostro caudal propagation of muscular activity. At high paper speed (on the right) it is evident that the onset of the EMG activity is in the left rectus abdominis (Rect Abd) muscle with ordered spreading to more rostral and caudal muscles. The burst duration is 455 ms. The propagation velocity is 6 m/s. Roman numerals indicate the order of recruitment of the different muscles. In parenthesis: the latency from the first muscle activated. Mylo: mylohyoideus; Masset: masseter; Delt: deltoideus; Interc: intercostalis; Parasp: paraspinales; Rect Fem: rectus femoris; Tib: tibialis; EMG: electromyography.

DD with movement disorders of the abdomen Spinal segmental myoclonus (SSM) consists in relatively long (up to 1000 ms) synchronous rhythmic jerks with a fairly constant frequency ranging from 20 to 180 per min, and confined to a group of muscles supplied by either one segment or several contiguous segments of the spinal cord [5]. Contrary to PSM, SSM is always symptomatic of a local pathology, either inflammatory, vascular, neoplastic or traumatic. It is believed to be the consequence of the spontaneous repetitive discharge of local segmental anterior horn cell pools because of the loss of inhibitory function of the disrupted interneurons. The “belly dance” syndrome is reported as a focal (diaphragmatic) flutter/dyskinesia with involuntary writhing movements and contractions of the abdominal wall, producing a slow multidirectional displacement of the umbilicus mimicking a belly dance [63]. The typical movement occurs in any body position both lying down and standing, without any particular circadian pattern and it has been reported to increase under physical or emotional stress [64,65]. Unlike PSM, the involuntary movements in the belly dance syndrome are confined to the abdominal muscles and occur at a

low frequency (mainly every 0.5e1 s) in repetitive, rhythmic or arrhythmic sequences. EMG discharges may last from 200 to 1000 ms and jerk-locked back averaging, when performed, resulted negative [66]. The syndrome may be idiopathic or occur after a spinal lesion [63], local trauma or abdominal pain [65,67,68], vitamin B12 deficiency, L-dopa treatment [66], antidopaminergic drugs [69] or pontine myelinolysis [64]. In any case, its overlap with spinal myoclonus [65,70,71] and with functional movement disorders remains unclear and current data are insufficient to categorize this disorder as a discrete clinical entity. Axial torsion dystonia may also produce flexor or extensor spasms of the trunk, typically appearing on action, especially on walking, and decreasing or disappearing when lying flat or relaxed [72]. Moreover, even if the movement disorder spreads to contiguous muscles (overflow dystonia), the pattern will not resemble the “up and down” hallmark of PMS. Finally, as stated above, clinical similarities bridge a link between PSM and tic disorders. Premonitory sensations and urge to perform have frequently been described also among cases of PSM. However, the ability to stop on volition has seldom been reported.

Please cite this article in press as: Antelmi E, Provini F, Propriospinal myoclonus: The spectrum of clinical and neurophysiological phenotypes, Sleep Medicine Reviews (2014), http://dx.doi.org/10.1016/j.smrv.2014.10.007

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Table 1 The spectrum of clinical and neurophysiological features of PSM subtypes. PSM at sleep onset

Symptomatic PSM

Functional PSM

Clinical features Population Increased by lying down Occurrence at sleepewake transition

Male > female; middle age In all patients In all patients

Male ¼ female; middle age Sporadically reported Not investigated

Occurrence during sleep

Usually not reported

Female > male; middle age In most of the patients Reported in few cases but never specifically investigated Frequently reported

Stimulus sensitive Premonitory sensations Neurophysiological features Pattern of muscles recruitment

Frequent Often reported

Frequent Sometimes reported

Co-contraction agonist antagonist Duration of muscles burst

It usually starts at the thoracic level and then simultaneously spreads up and down into contiguous spinal levels Frequent Usually 100e300 ms

It usually starts on superior rectus abdominis and then simultaneously spreads up and down into contiguous spinal levels Frequent Usually 100e300 ms, but can be longer

Velocity of muscles recruitment

1.5e3 m/s (from 1 to 15 m/s)

1.5e3 m/s (from 1 to 16 m/s)

Involvement of neck muscles Involvement of cranial muscles BP Latency after stimulus Lab and instrumental examinations Lab abnormalitiesa Spinal MRI abnormalities DTI sequences abnormalities

Reported Usually not reported (few exceptions) No

Propriospinal myoclonus: The spectrum of clinical and neurophysiological phenotypes.

Propriospinal myoclonus (PSM) is a rare type of spinal myoclonus characterized by muscle jerks that usually start in the midthoracic segments and then...
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