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Background: Motor unit number index (MUNIX) is a validated electrophysiological biomarker in amyotrophic lateral sclerosis. MUNIX studies in spinal muscular atrophy (SMA) are limited.Methods: Later-onset SMA children (n = 13; three SMN2 copy number) were evaluated for Hammersmith Motor Function Scale Expanded (HMFSE) and MUNIX of right abductor pollicis brevis (APB) and abductor digiti minimi (ADM) muscles. Age-matched healthy controls (n = 8) were enrolled to obtain normative APB and ADM MUNIX values.Results: Mean APB and ADM MUNIX values in SMA subjects were significantly reduced (P < .001) compared with controls. HMFSE scores strongly correlated with ADM MUNIX (r 0.63).Conclusions: APB and ADM muscle MUNIX studies are feasible in SMA type 2 children. ADM MUNIX correlated with disease severity on motor function testing. MUNIX studies in later-onset SMA could be a potential biomarker of motor neuron loss. [ABSTRACT FROM AUTHOR]

Introduction: This study's objective was to evaluate quantitative electromyography (QEMG) using multiple-motor-unit (multi-MUP) analysis in Duchenne muscular dystrophy (DMD).Methods: Ambulatory DMD boys, aged 5-15 years, were evaluated with QEMG at 6-month intervals over 14 months. EMG was performed in the right biceps brachii (BB) and tibialis anterior (TA) muscles. Normative QEMG data were obtained from age-matched healthy boys. Wilcoxon signed-rank tests were performed.Results: Eighteen DMD subjects were enrolled, with a median age of 7 (interquartile range 7-10) years. Six-month evaluations were performed on 14 subjects. QEMG showed significantly abnormal mean MUP duration in BB and TA muscles, with no significant change over 6 months.Conclusions: QEMG is a sensitive electrophysiological marker of myopathy in DMD. Preliminary data do not reflect a significant change in MUP parameters over a 6-month interval; long-term follow-up QEMG studies are needed to understand its role as a biomarker for disease progression. Muscle Nerve 56: 1361-1364, 2017. [ABSTRACT FROM AUTHOR]

Introduction/Aims: Objective outcome measures in children undergoing treatment for chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) are lacking. The aim of the study was to record serial grip strength and motor nerve conduction studies to assess interval change. Methods: This was a retrospective review of 16 children (8 females and 8 males; median age, 9.7 years; interquartile range, 6–13 years) with CIDP followed at a tertiary children's hospital from 2013 to 2021. Subjects were treated with intravenous immunoglobulin (IVIG). Right and left grip strength measurements were obtained at each clinic visit using a handheld dynamometer. Annual right median motor nerve conduction study data were recorded during the study period. Results: Mean duration of follow‐up was 2.9 years. Grip strength (right: 0.19 kg/month, p < 0.001; left 0.23 kg/month, p < 0.001) and median F‐wave latencies (−0.23/month, p = 0.015) showed significant improvement over time. Akaike information criterion showed time + IVIG frequency <21 days as best fit for grip strength and distal compound muscle action potential amplitude. Discussion: Our study results indicate serial grip strength measurements are a feasible and objective way to assess motor strength improvement in children with CIDP receiving immunotherapy. [ABSTRACT FROM AUTHOR]

Introduction: Stimulated jitter analysis (stim-JA) using a concentric needle electrode is a technique used to study the neuromuscular junction (NMJ) without voluntary activation. Our objective was to study the diagnostic sensitivity, specificity, and feasibility of stim-JA in infants and children with suspected NMJ defects.Methods: Sixteen infants and young children ages 2 months to 17 years with suspected NMJ disorders were evaluated using stim-JA over a period of 12 months.Results: Subjects with suspected NMJ defects and abnormal stim-JA subsequently had laboratory confirmation of myasthenia gravis (n = 5) and infant botulism (n = 2). Turnaround time for confirmatory laboratory tests was 6.0 ± 4.3 days, whereas stim-JA results were available immediately. All subjects tolerated stim-JA well without complications or need for sedation.Conclusions: Stim-JA is a sensitive and safe first-line diagnostic test for evaluation of suspected pediatric NMJ disorders. Stim-JA results precede assay results and may guide early treatment. [ABSTRACT FROM AUTHOR]

Introduction: Clinical and electrophysiological studies to measures disease activity in juvenile myasthenia gravis (JMG) are limited.Methods: Retrospective review of the clinical profile, Myasthenia Gravis Foundation of America (MGFA) scores, serial stimulated jitter analysis (Stim-JA) of the orbicularis oculi muscle, grip strength, and spirometry of patients with JMG who were followed in a multidisciplinary clinic was performed.Results: Thirteen patients with JMG (9 females) with mean age of 13.2 ± 4.8 years and follow-up duration of 25.3 ± 8.3 months (range, 6-39) with ≥ 2 Stim-JA recordings were included. The mean jitter, mean percentage of apparent single-fiber action potentials (%ASFAP) with increased jitter, and mean %ASFAP with blocking at baseline values (77.3 ± 54.7 µs, 64.3% ± 35.8%, 39% ± 38.6%, respectively) and at follow-up (53 ± 45.4 µs, 51.2% ± 34.5%, 17% ± 29.4%, respectively) were abnormal; however, no statistically significant interval difference was noted. The electrophysiological data correlated significantly with Myasthenia Gravis Foundation of America (MGFA) class. Grip strength and spirometry did not correlate with MGFA class.Discussion: Stimulated jitter values are sensitive biomarkers in JMG. Muscle Nerve 58: 729-732, 2018. [ABSTRACT FROM AUTHOR]