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Introduction/aims: Reliable neurophysiological markers in amyotrophic lateral sclerosis (ALS) are of great interest. The compound muscle action potential (CMAP) amplitude has been a conventional marker, although it is greatly influenced by the electrode position. We propose the far-field potential of the CMAP (FFP-CMAP) as a new neurophysiological marker in ALS., Methods: Patients with ALS and age-matched healthy controls were enrolled. We used a proximal reference (pref) in addition to the conventional distal reference (dref). Routine CMAP was recorded from the belly-dref lead and FFP-CMAP from the dref-pref lead for the ulnar and tibial nerves. Multiple point stimulation motor unit number estimation (MUNE) was also examined in the ulnar nerve. Inter-rater reproducibility was evaluated by two examiners, and some patients were followed up every 3 mo for 1 y., Results: We tested 17 patients with ALS and 10 controls. The amplitudes of routine CMAP and FFP-CMAP in the ulnar and tibial nerves, and hypothenar MUNE value in the ulnar nerve were significantly decreased in ALS compared to controls. Ulnar FFP-CMAP achieved the highest inter-rater intraclass correlation coefficient (ICC) value (0.942) when compared with routine CMAP (0.880) and MUNE (0.839). The tibial FFP-CMAP had a higher ICC value (0.986) than the routine CMAP (0.697). In this way, the FFP-CMAP showed high inter-rater reproducibility because its shape was not much influenced by the electrode position. During 1-y follow-up, decline of CMAP, FFP, and MUNE showed significant correlations with the Amyotrophic Lateral Sclerosis Functional Rating Scale - Revised (ALSFRS-R)., Discussion: The FFP-CMAP shows promise as a reliable marker for ALS., (© 2023 Wiley Periodicals LLC.)

We previously reported a new quantitative analysis of single-channel surface electromyography (EMG), the "clustering index method" (CI method), in the tibialis anterior muscle, which achieved sufficiently good sensitivity to detect neurogenic or myogenic abnormalities. The window width is a fundamental parameter of the CI method, and was arbitrarily set at 15 ms in that study. In this study, we searched for the most appropriate window width using expanded patient data. The data from our previous study were reanalyzed, and new patients were enrolled. Window width in the CI method was changed from 5 to 27.5 ms with a step of 2.5 ms. For each window width, Z-score values of individual subjects were calculated and the diagnostic yield was investigated. We enrolled 67 controls, 29 subjects with neurogenic disorders, and 39 with myogenic disorders. When the window width was set at 22.5 ms, the highest sensitivity was achieved both for neurogenic (97%) and myogenic (72%) disorders, with a specificity of 97%. Seven of 10 patients with inclusion body myositis were also abnormal. Reliable results were obtained by collecting 15 epochs per subject. There are two conflicting effects that appear to be best balanced at a window width of 22.5 ms: a wider width decreases the chance that a motor unit potential (MUP) is divided into two adjacent windows, and a narrower width reduces the possibility that an MUP firing at a low-frequency is counted twice by the differential sequences. CI is promising as a non-invasive method to diagnose neuromuscular disorders., (© 2020 Wiley Periodicals LLC.)

Introduction: We sought to evaluate the reproducibility of the motor unit number index (MUNIX) and MScanFit motor unit number estimation (MScan) when recording was performed over intrinsic hand muscles., Methods: The compound muscle action potential (CMAP) amplitude, MUNIX, and MScan were measured from the abductor pollicis brevis (APB), first dorsal interosseous (FDI), and abductor digit minimi (ADM) muscles from 15 healthy volunteers on three different occasions., Results: The reproducibility of CMAP amplitudes was excellent, with intraclass correlation coefficients (ICC) of 0.86 (APB), 0.90 (FDI), and 0.96 (ADM). Motor unit number index (ICC APB 0.73, ICC FDI 0.85, ICC ADM 0.85) and MScan (ICC APB 0.86, ICC FDI 0.83, ICC ADM 0.81) were highly reproducible across the three muscles. There were no significant correlations between MUNIX and MScan coefficients of variation (CV) and CMAP amplitude CVs., Discussion: Reproducibility of MUNIX and MScan was not significantly different across the intrinsic hand muscles and was independent of CMAP amplitude variability., (© 2020 Wiley Periodicals, Inc.)

Introduction: Needle electromyography (EMG) has been an important diagnostic tool, although discomfort may limit its use in some children. We investigated the diagnostic utility of the clustering index (CI) method, a quantitative analysis for surface EMG (SEMG), in children., Methods: SEMG was recorded from the tibialis anterior muscle. Discriminant analysis between patients with neurogenic disorders and patients with myopathy was performed for whole epochs by using the CI and area values., Results: Forty-five children (29 with myopathy, 16 with neurogenic disorders; age 9 ± 3.9 years) were enrolled. The mean discriminant function value of the neurogenic group was 0.58 ± 0.88 (-0.48-2.30), whereas that of the myopathic group was -0.55 ± 0.70 (-2.38-0.68). When the cutoff value was set at the limit of the other group, 17 of 29 children with myopathy and 7 of 16 children with neurogenic disorders were correctly classified., Discussion: The CI method can be a useful noninvasive diagnostic tool in children with neuromuscular disorders. Muscle Nerve 58:824-827, 2018., (© 2018 Wiley Periodicals, Inc.)

Introduction: Reproducibility of the multiple point stimulation motor unit number estimation (MPS-MUNE) technique was compared with the recently developed motor unit number index (MUNIX) technique., Methods: MPS-MUNE and MUNIX were performed on 15 healthy subjects at 3 different time-points by the same examiner. Reproducibility was analyzed using intraclass correlation coefficient (ICC) and coefficient of variation (CV)., Results: ICC values for MUNIX and MPS-MUNE were excellent across 3 tests (0.80 and 0.77, respectively), although CV values were significantly lower for MUNIX than MPS-MUNE (P < 0.01). In addition, test-retest reproducibility was better for MUNIX, a finding largely attributable to poor reproducibility of the single motor unit action potential area. MUNIX (R = -0.48, P < 0.05) and MPS-MUNE (R = -0.53, P < 0.05) were significantly correlated with age., Discussion: MUNIX demonstrated better intrarater reproducibility and may be a more reliable neurophysiological biomarker than MPS-MUNE. Muscle Nerve 58: 660-664, 2018., (© 2018 Wiley Periodicals, Inc.)

Introduction: Contamination by far-field potentials (FFPs) may interfere with motor unit number estimation (MUNE) in the ulnar nerve., Methods: Surface motor unit potentials (SMUPs) from 29 spinal and bulbar muscular atrophy (SBMA) patients and 27 control subjects were classified into SMUPs from the abductor digiti minimi muscle (ADM SMUPs) or non-ADM SMUPs, based on the waveform patterns from 3-channel recordings., Results: The mean areas of the ADM SMUPs and non-ADM SMUPs in control subjects were 219.0 ± 131.3 and 63.7 ± 48.5 μVms, respectively. In SBMA patients they were 1988.9 ± 999.4 and 222.7 ± 125.7 μVms, respectively. The percentages of non-ADM SMUPs were 68 ± 22% in controls and 84 ± 15% in SBMA patients., Conclusions: Non-ADM SMUPs generated mainly by FFPs often had a negative onset in the routine lead and were indistinguishable from ADM SMUPs. More frequent exclusion of smaller non-ADM SMUPs in controls by size criteria would reduce the diagnostic yield of MUNE., (© 2013 Wiley Periodicals, Inc.)

Introduction: Far-field potentials (FFPs) from muscles other than the abductor digiti minimi (ADM) may interfere with motor unit number estimation (MUNE) from that muscle., Methods: We identified the origin of each surface motor unit potential (SMUP) during hypothenar MUNE using the multiple point stimulation method in 20 control subjects by recording from individual ulnar-innervated muscles with a common proximal reference (pref)., Results: ADM SMUPs comprised 39.0% of the accepted SMUPs, followed by those from the fourth dorsal interosseous muscle (14.0%), the fourth lumbrical muscle (9.2%), and the second and third palmar interosseous muscles (8.8% each). The percentage of ADM SMUPs varied from 18% to 73% of accepted SMUPs among individual subjects. Accepted non-ADM SMUPs were usually much smaller than ADM SMUPs, and many more non-ADM SMUPs were excluded due to their small size., Conclusions: A large contribution from non-ADM or non-hypothenar SMUPs obscures the meaning of the MUNE value., (© 2013 Wiley Periodicals, Inc.)

Introduction: The frequent observation of high-amplitude and long-duration motor unit potentials (MUPs) in inclusion body myositis (IBM) is problematic, because it may lead to a misdiagnosis of amyotrophic lateral sclerosis (ALS)., Objective: To document the diagnostic utility of EMG from the flexor digitorum profundus (FDP) muscle for IBM., Methods: Quantitative analyses of MUP parameters were performed in the FDP and biceps brachii (BB) muscles from 7 biopsy-confirmed IBM patients., Results: In the FDP muscle, all MUP parameters were significantly decreased in IBM patients, which indicated the predominance of low-amplitude and short-duration MUPs in this muscle. In the BB muscle, most parameters were increased, suggesting the frequent contamination of high-amplitude and long-duration MUPs., Conclusions: Low-amplitude MUPs in the FDP muscle indicate the presence of an advanced myopathy in this muscle that was extremely weak for all subjects. Examining the FDP muscle would reduce the chance of misdiagnosing IBM as ALS., (Copyright © 2012 Wiley Periodicals, Inc.)

Introduction: The role of fasciculation potentials (FPs) in the diagnosis of amyotrophic lateral sclerosis (ALS) has been underrated. The Awaji algorithm has restored the value of FPs. Our aim was to test the diagnostic yield of the Awaji algorithm, with consideration of FPs., Methods: Subjects consisted of 139 consecutive ALS patients retrospectively enrolled over 5 years. At presentation we evaluated the diagnostic categories using the revised El Escorial Criteria (R-EEC) and the Awaji algorithm., Results: The percentage of patients classified as confirmed ALS, clinically probable (laboratory-supported), or higher was 43% using the R-EEC and 37% using the Awaji algorithm. Thirteen patients with upper motor neuron signs only in one body region showed a decrease in their category using the Awaji algorithm. FPs were observed in 89% of ALS patients and were frequent in proximal muscles., Conclusion: The sensitivity of the Awaji algorithm is lower than that of the R-EEC., (Copyright © 2011 Wiley Periodicals, Inc.)

Introduction: A reliable electrophysiological marker for clinical trials is increasingly needed in spinal and bulbar muscular atrophy (SBMA). We previously developed a quantitative analysis method for surface electromyography (SEMG), the clustering index (CI) method. Our purpose was to test the utility of the CI method for evaluating lower motor neuron involvement in SBMA patients., Methods: Subjects included 29 SBMA patients and 27 healthy controls. The recording electrode was placed over the abductor digiti minimi (ADM) muscle with a proximal reference. The Z-score, based on the CI method, was compared with compound muscle action potential (CMAP) amplitude and motor unit number estimation (MUNE), with regard to sensitivity., Results: The Z-scores of the CI method, CMAP amplitude, and MUNE were abnormal in 100%, 72%, and 93% of the patients, respectively. Interrater reliability of the CI method was sufficiently high., Conclusion: The CI method is promising as a non-invasive electrophysiological marker in SBMA., (Copyright © 2011 Wiley Periodicals, Inc.)

Introduction: The compound muscle action potential (CMAP) following ulnar nerve stimulation receives a considerable contribution from far-field potentials (FFPs), although their origin is not entirely clear. We investigated this issue using voluntary contractions., Methods: In 7 control subjects, we placed multiple recording electrodes over the motor points of ulnar-innervated muscles. We asked the subjects to perform a weak movement corresponding to the action of each muscle, and identified the single motor unit potentials (MUPs) from that muscle. We summed the MUPs from each individual muscle and reconstructed the CMAPs., Results: The reconstructed CMAPs coincided well with the actual ones. The N1, P1, and early N2 components of the FFPs were generated primarily by palmar, but also by dorsal, interosseous muscles. The abductor digiti minimi muscle usually generated positive-negative biphasic FFPs, and the negative FFP generated the late N2 component., Conclusions: These results should prompt a revision of the theory of FFP generation., (Copyright © 2010 Wiley Periodicals, Inc.)

The compound muscle action potential from the abductor digiti minimi muscle is bi-lobed, and its second peak is formed by far-field potentials (FFPs). We investigated their origin in two patients with ulnar neuropathy at the wrist that spared the hypothenar muscles. FFPs were lost or distorted, which indicated that the deep motor branch-innervated muscles, such as the interossei, mainly contributed to the FFPs, especially to their initial N1 and steep following P1 components.