Myoclonus:A diagnostic challenge

Myoclonus is een frequent voorkomende hyperkinetische bewegingsstoornis die wordt gekenmerkt door spierschokken (positieve myoclonus) en/of het kortdurend wegvallen van de spiertonus (negatieve myoclonus). De klinische presentatie van myoclonus is heel divers. De schokken kunnen in één of meerdere lichaamsdelen optreden of gegeneraliseerd zijn. Myoclonus kan optreden in het gelaat, de nek, romp en de ledematen. Het kan in rust of juist bij actie optreden en wel of niet stimulusgevoelig zijn. Over het algemeen belemmert myoclonus patiënten ernstig in hun dagelijks functioneren, zoals bij eten/drinken, schrijven en lopen. Myoclonus heeft vele oorzaken, zowel verworden als genetisch. Voor het vaststellen van de onderliggende oorzaak en het bepalen van de juiste behandeling is het belangrijk myoclonus te herkennen en te onderscheiden van andere bewegingsstoornissen zoals bijvoorbeeld tremor en chorea. Na het herkennen kan myoclonus op basis van een anatomische classificatie worden ingedeeld in subtypes, i.e. naar de plaats in het zenuwstelsel waar de schokken ontstaan. Dit zijn corticale (hersenschors), subcorticale (diepe hersenkernen/hersenstam), spinale (ruggenmerg) en perifere (zenuwen/spieren) myoclonus. Daarnaast kunnen schokken ook een uiting zijn van een functionele (psychogene) stoornis. Door myoclonus naar anatomische classificatie te groeperen kan diagnostiek gericht ingezet worden. Dit proefschrift biedt een nieuw diagnostische aanpak voor patiënten met myoclonus. Het beschrijft de uitdagingen en het belang van het nauwkeurig klinisch fenotyperen van zowel motorische als niet-motorische symptomen en de classificatie van het anatomisch myoclonus subtype. Het klinisch neurofysiologisch onderzoek heeft een belangrijke toegevoegde waarde naast de klinische beoordeling in de (sub)classificatie van myoclonus

Distribution and coexistence of myoclonus and dystonia as clinical predictors of SGCE mutation status: a pilot study

Introduction: Myoclonus-dystonia (M-D) is a young onset movement disorder typically involving myoclonus and dystonia of the upper body. A proportion of the cases are caused by mutations to the autosomal dominantly inherited, maternally imprinted, epsilon-sarcoglycan gene (SGCE). Despite several sets of diagnostic criteria, identification of patients most likely to have an SGCE mutation remains difficult. Methods: Forty consecutive patients meeting pre-existing diagnostic clinical criteria for M-D underwent a standardized clinical examination (20 SGCE mutation positive and 20 negative). Each video was reviewed and systematically scored by two assessors blinded to mutation status. In addition, the presence and coexistence of myoclonus and dystonia was recorded in four body regions (neck, arms, legs, and trunk) at rest and with action. Results: Thirty-nine patients were included in the study (one case was excluded owing to insufficient video footage). Based on previously proposed diagnostic criteria, patients were subdivided into 24 "definite," 5 "probable," and 10 "possible" M-D. Motor symptom severity was higher in the SGCE mutation-negative group. Myoclonus and dystonia were most commonly observed in the neck and upper limbs of both groups. Truncal dystonia with action was significantly seen more in the mutation-negative group (p <0.05). Coexistence of myoclonus and dystonia in the same body part with action was more commonly seen in the mutation-negative cohort (p <0.05). Conclusion: Truncal action dystonia and coexistence of myoclonus and dystonia in the same body part with action might suggest the presence of an alternative mutation in patients with M-D

Natural course of Myoclonus-Dystonia in adulthood: stable motor signs but increased psychiatry

Myoclonus‐dystonia (M‐D) is a rare hyperkinetic movement disorder characterized by upper body–predominant myoclonus and dystonia.1 A large proportion of cases are caused by autosomal‐dominant inherited mutations in the SGCE gene. In addition to the motor manifestations, psychiatric disorders are frequently reported.2 Several studies have suggested that they may form a primary component of the M‐D phenotype.3, 4 This study represents the first long‐term follow‐up study of both motor and psychiatric symptomatology in adults with M‐D (SGCE mutation), providing further insights into the natural history of M‐D and enabling more prognostic information

Skater's Cramp:A Possible Task-Specific Dystonia in Dutch Ice Skaters

Background Skater's cramp is an involuntary lower leg movement in skilled speed skaters. We aim to evaluate whether skater's cramp is compatible with task-specific dystonia. Methods A case-control study tested 5 speed skaters exhibiting symptoms of skater's cramp and 5 controls. Affected skaters completed a standardized questionnaire and neurological examination. Video analyses included skating normally, intensely, and with extra mass around the skater's ankles. An Inertial Motion Capturing (IMC) device mounted on both skates provided angular velocity data for both feet. Results Median time of onset of skater's cramp occurred after 12 (range 3-22) years of speed skating. Skater's cramp appeared as task specific; its onset was sudden and correlated to stress and aberrant proprioception. Symptoms presented acutely and consistently during skating, unilaterally in 4 and bilaterally in 1 skater. Visually, skater's cramp was an active, patterned, and person-specific jerking of a skater's foot, either exo- or endorotationally. It presented asymmetrically, repeating persistently as the foot neared the end of the swing phase. The skater's affected leg had a longer swing phase (median, 1.37 [interquartile range {IQR}, 0.35]/1.18 [IQR, 0.24] seconds; P 0.05). No significant differences between legs were detected in the control group. Conclusions Observed clinical, visual, and kinematic data could be an early and tentative indication of task-specific dystonia

Nomenclature of Genetically Determined Myoclonus Syndromes:Recommendations of the International Parkinson and Movement Disorder Society Task Force

Genetically determined myoclonus disorders are a result of a large number of genes. They have wide clinical variation and no systematic nomenclature. With next-generation sequencing, genetic diagnostics require stringent criteria to associate genes and phenotype. To improve (future) classification and recognition of genetically determined movement disorders, the Movement Disorder Society Task Force for Nomenclature of Genetic Movement Disorders (2012) advocates and renews the naming system of locus symbols. Here, we propose a nomenclature for myoclonus syndromes and related disorders with myoclonic jerks (hyperekplexia and myoclonic epileptic encephalopathies) to guide clinicians in their diagnostic approach to patients with these disorders. Sixty-seven genes were included in the nomenclature. They were divided into 3 subgroups: prominent myoclonus syndromes, 35 genes; prominent myoclonus syndromes combined with another prominent movement disorder, 9 genes; disorders that present usually with other phenotypes but can manifest as a prominent myoclonus syndrome, 23 genes. An additional movement disorder is seen in nearly all myoclonus syndromes: ataxia (n = 41), ataxia and dystonia (n = 6), and dystonia (n = 5). However, no additional movement disorders were seen in related disorders. Cognitive decline and epilepsy are present in the vast majority. The anatomical origin of myoclonus is known in 64% of genetic disorders: cortical (n = 34), noncortical areas (n = 8), and both (n = 1). Cortical myoclonus is commonly seen in association with ataxia, and noncortical myoclonus is often seen with myoclonus-dystonia. This new nomenclature of myoclonus will guide diagnostic testing and phenotype classification. (c) 2019 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society

Electrophysiologic testing aids diagnosis and subtyping of myoclonus

OBJECTIVE: To determine the contribution of electrophysiologic testing in the diagnosis and anatomical classification of myoclonus. METHODS: Participants with a clinical diagnosis of myoclonus were prospectively recruited, each undergoing a videotaped clinical examination and battery of electrophysiologic tests. The diagnosis of myoclonus and its subtype was reviewed after 6 months in the context of the electrophysiologic findings and specialist review of the videotaped clinical examination. RESULTS: Seventy-two patients with myoclonus were recruited. Initial clinical anatomical classification included 25 patients with cortical myoclonus, 7 with subcortical myoclonus, 2 with spinal myoclonus, and 15 with functional myoclonic jerks. In 23 cases, clinical anatomical classification was not possible because of the complexity of the movement disorder. Electrophysiologic testing was completed in 66, with agreement of myoclonus in 60 (91%) and its subtype in 28 (47%) cases. Subsequent clinical review by a movement disorder specialist agreed with the electrophysiologic findings in 52 of 60; in the remaining 8, electrophysiologic testing was inconclusive. CONCLUSIONS: Electrophysiologic testing is an important additional tool in the diagnosis and anatomical classification of myoclonus, also aiding in decision-making regarding therapeutic management. Further development of testing criteria is necessary to optimize its use in clinical practice