The function of the neuromuscular junction in children is amenable to electrophysiological testing. Of the two tests available, repetitive nerve stimulation is uncomfortable and has a reduced ...sensitivity compared with single-fibre methodology. The latter is the method of choice, recording the variability in neuromuscular transmission as a value called jitter. It can be performed by voluntary activation of the muscle being examined, which is not suitable in children, or by stimulation techniques. A modification of these techniques, called Stimulated Potential Analysis with Concentric needle Electrodes (SPACE), is well tolerated and can be performed while the child is awake. It has a high sensitivity (84%) for the diagnosis of neuromuscular transmission disorders, the majority of which are myasthenic syndromes, and a moderate specificity (70%). The latter can be improved by the exclusion of neurogenic causes and the determination of the degree of jitter abnormality. Minor jitter abnormalities, under 115% of the upper limit of normal, are usually caused by myopathies with an associated neuromuscular transmission disorder, whereas levels higher than this value are usually associated with one of the myasthenic conditions.
ABSTRACT
A screening test is required to diagnose disorders of the neuromuscular junction (NMJ) in children. This Review describes the development of stimulation potential analysis with concentric ...needle electrodes (SPACE). This nomenclature was chosen to distinguish the technique from single‐fiber methodology because of the difficulties in identifying single‐fiber potentials in most studies, particularly those with the most severe abnormalities of the NMJ. Performed on orbicularis oculi in children with proven or probable disorders of the NMJ, it demonstrated a sensitivity of 84%, specificity of 71%, negative predictive value of 95%, and positive predictive value of 36%. It is well tolerated and within the capability of any clinical neurophysiologist. When combined with a full electrodiagnostic examination, SPACE provides invaluable information about children with NMJ disorders, whose diagnosis often is difficult. Muscle Nerve 56: 841–847, 2017
•Standards for EMG and Neurography are suggested.•Electrophysiological tests in Pediatric practice are summarized.•Implementation and clinical utility of less common methods for EMG and neurography ...are presented.
This document is an update and extension of ICCN Standards published in 1999. It is the consensus of experts on the current status of EMG and Neurography methods. A panel of authors from different countries with different approach to routines in neurophysiological methods was chosen based on their particular interest and previous publications. Each member of the panel submitted a section on their particular area of interest and these submissions were circulated among the panel members for edits and comments. This process continued until a consensus was reached.
The document covers EMG topics such as conventional EMG, Macro EMG, applications of surface EMG and electrical impedance myography. Single Fiber EMG is not included, since it is the topic in a separate IFCN document. A neurography section covers topics such as motor and sensory neurography, F wave recordings, H-reflex, short segment recordings, CMAP scan and motor unit number methods. Other sections cover repetitive nerve stimulation and Pediatric electrodiagnostic testing.
Each method includes a description of methodologies, pitfalls, and the use of reference values. Clinical applications accompany some of these sections.
•Pediatric EMG is an essential part of the workup of children with neuromuscular disorders.•The paucity of normal values in the <3 years old poses a limitation in the analysis of their tests.•The ...e-norms method is a fast and efficient method to derive a lab’s own normal values.
This work describes our efforts to obtain nerve conduction studies normal values in a pediatric cohort between birth and 3 years of age using the extrapolated norms or e-norms method. Interpretation of these studies poses major challenges when no reliable normal values can be found in the literature.
The e-norms method was used to derive a reference range of upper and lower extremity sensory and motor nerve conductions normal values from a pediatric cohort referred to an EMG Laboratory for nerve conduction studies.
E-norms were calculated for Median, Ulnar, Superficial Peroneal, Sural, and Medial Plantar sensory studies, and for Median, Ulnar, Peroneal, and Tibial motor studies.
Pediatric electrodiagnostic testing is a very challenging undertaking. The ability to obtain and use normal values from the neurophysiologist’s own referral pool adds great value to their diagnostic work-up.
EMG and nerve conduction studies can yield invaluable information in the diagnostic work-up of young infants. Using the e-norms method improves on the analysis and interpretation of electrophysiological studies in this age group.
ABSTRACT
Introduction: The diagnosis of myasthenia gravis in very young infants is a challenging one. In young infants, stimulated single‐fiber electromyography (StimSFEMG) is the most appropriate ...technique, but it has serious limitations due to the absence of reference values in this subpopulation. Here we present our efforts to derive a reference range of jitter in a patient cohort of infants <3 years of age using the extrapolated norms, or e‐norms, technique. Methods: The e‐norms method was used to calculate jitter mean consecutive difference (MCD) descriptive statistics for children <3 years of age. Results: The e‐norms derived jitter upper MCD limit was 45 μs in children <1 year, 33 μs in those <2 years, and 26 in those <3 years of age. Conclusion: In the absence of jitter reference values for the very young, the e‐norms method can be used as an alternative to derive these values from laboratory cohorts. Muscle Nerve 55: 51–54, 2017
Highlights • Stimulated concentric needle electrode-jitter was recorded in 878 children, of whom 106 had neuromuscular junction disorders. • The technique is well tolerated in waking children using ...topical anaesthetic only. • Sensitivity is 84% for primary neuromuscular junction disorders; negative predictive value is 96%.
We report 2 families with undiagnosed recessive presynaptic congenital myasthenic syndrome (CMS). Whole exome or genome sequencing identified segregating homozygous variants in VAMP1: ...c.51_64delAGGTGGGGGTCCCC in a Kuwaiti family and c.146G>C in an Israeli family. VAMP1 is crucial for vesicle fusion at presynaptic neuromuscular junction (NMJ). Electrodiagnostic examination showed severely low compound muscle action potentials and presynaptic impairment. We assessed the effect of the nonsense mutation on mRNA levels and evaluated the NMJ transmission in VAMP1lew/lew mice, observing neurophysiological features of presynaptic impairment, similar to the patients. Taken together, our findings highlight VAMP1 homozygous mutations as a cause of presynaptic CMS. Ann Neurol 2017;81:597–603
Abstract Nerve conduction studies and needle EMG in children under two years of age present a considerable technical challenge to the neurophysiologist. However, with adaptations of both the ...equipment used and the methods applied, useful results can be obtained in most cases. Normative data exists against which results can be compared exists but are not comprehensive and often the experience of the practitioner is most important for interpretation of the results. Conditions, which are diagnosed fall under the broad categories of disorders of nerve, anterior horn cell, muscle or neuromuscular junction, with certain conditions seen more commonly than in older children. Examples include hypomyelinating neuropathy, SMARD, myotonic dystrophy, congenital myasthenic syndrome, and neonatal brachial plexopathy. While few practitioners perform EMG in children so young the rewards may be considerable with information obtained that is almost always important in the management of the children. It is feasible for any trained neurophysiologists to do and more should be encouraged to offer this service which comprises one quarter of the author’s clinical case load.
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