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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: 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]