Motor Unit Number Index (MUNIX) detects motor neuron loss in pre-symptomatic muscles in Amyotrophic Lateral Sclerosis |
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Authors: | Christoph Neuwirth Paul E. Barkhaus Christian Burkhardt José Castro David Czell Mamede de Carvalho Sanjeev Nandedkar Erik Stålberg Markus Weber |
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Affiliation: | 1. Neuromuscular Diseases Unit/ALS Clinic, Kantonsspital St. Gallen, St. Gallen, Switzerland;2. Medical College of Wisconsin, Milwaukee, WI, USA;3. Department of Neurosciences, Hospital de Santa Maria, Instituto de Medicina Molecular, Faculty of Medicine, University of Lisbon, Lisbon, Portugal;4. Kantonsspital Winterthur, Winterthur, Switzerland;5. Natus Medical Inc, Middleton, WI, USA;6. Institute of Neurosciences, Uppsala University, Department of Clinical Neurophysiology, University Hospital, Uppsala, Sweden;7. Department of Neurology, University Hospital Basel, Basel, Switzerland |
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Abstract: | ObjectiveMotor Unit Number Index (MUNIX) is a quantitative neurophysiological measure that provides an index of the number of lower motor neurons supplying a muscle. It reflects the loss of motor neurons in patients with Amyotrophic Lateral Sclerosis (ALS). However, it is unclear whether MUNIX also detects motor unit loss in strong, non-wasted muscles.MethodsThree centres measured MUNIX in 49 ALS patients every three months in six different muscles (abductor pollicis brevis, abductor digiti minimi, biceps brachii, tibialis anterior, extensor digitorum brevis, abductor hallucis) on the less affected side. The decline of MUNIX in initially non-wasted, clinically strong muscles (manual muscle testing, MMT grade 5) was analysed before and after onset of weakness.ResultsIn 49 subjects, 151 clinically strong muscles developed weakness and were included for analysis. The average monthly relative loss of MUNIX was 5.0% before and 5.6% after onset of weakness. This rate of change was significantly higher compared to ALS functional rating scale (ALSFRS-R) and compound muscle action potential (CMAP) change over 12 months prior to the onset of muscle weakness (p = 0.024).ConclusionMUNIX is an electrophysiological marker that detects lower motor neuron loss in ALS, before clinical weakness becomes apparent by manual muscle testing.SignificanceThis makes MUNIX a good biomarker candidate for disease progression and possibly pharmacodynamics responds. |
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Keywords: | ADM abductor digiti minimi muscle AH abductor hallucis muscle ALS Amyotrophic Lateral Sclerosis ALSFRS-R revised amyotrophic lateral sclerosis functional rating scale APB abductor pollicis brevis muscle BB biceps brachii muscle CI Confidence Intervals CMAP compound muscle action potential EDB extensor digitorum brevis muscle FDI first dorsal interosseus muscle LMN lower motor neuron MMT manual muscle testing MUNE motor unit number estimation MUNIX motor unit number index SD standard deviation TA tibialis anterior muscle UMN upper motor neuron MUNIX Pre-symptomatic ALS Biomarker Multicentre ALSFRS-R |
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