Motor unit number index and compound muscle action potential amplitude. 2019

H Bostock, and A B Jacobsen, and H Tankisi
Department of Clinical Neurophysiology, Aarhus University Hospital, Aarhus, Denmark; UCL Queen Square Institute of Neurology, Queen Square, London, UK. Electronic address: h.bostock@ucl.ac.uk.

MUNIX (motor unit number index), derived from the compound muscle action potential (CMAP) and surface EMG interference pattern (SIP) has become popular as a substitute for motor unit number estimation (MUNE). This study was undertaken to determine why, in recent recordings from amyotrophic lateral sclerosis (ALS) patients and healthy controls, we found that MUNIX values resembled CMAP amplitudes more closely than MUNE values. The relationship between MUNIX and CMAP and SIP amplitudes was investigated by a theoretical analysis and by reanalysing the data from the previous study. Theory indicates that when motor unit potentials overlap extensively, information about motor unit size and number is lost, and MUNIX depends only on CMAP area and power. Accordingly, MUNIX values were found to be sensitive to changes in CMAP amplitude but insensitive to changes in SIP amplitude. The reproducibility of MUNIX measurements in healthy controls was found to depend almost entirely on correlation with CMAP properties. MUNIX gives misleading information about motor unit numbers in healthy controls, and provides little information about loss of motor units in ALS patients beyond that given by simple CMAP amplitude measurements. MUNIX should not be interpreted as a MUNE method.

UI MeSH Term Description Entries
D008297 Male Males
D008875 Middle Aged An adult aged 45 - 64 years. Middle Age
D009431 Neural Conduction The propagation of the NERVE IMPULSE along the nerve away from the site of an excitation stimulus. Nerve Conduction,Conduction, Nerve,Conduction, Neural,Conductions, Nerve,Conductions, Neural,Nerve Conductions,Neural Conductions
D004576 Electromyography Recording of the changes in electric potential of muscle by means of surface or needle electrodes. Electromyogram,Surface Electromyography,Electromyograms,Electromyographies,Electromyographies, Surface,Electromyography, Surface,Surface Electromyographies
D005260 Female Females
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000200 Action Potentials Abrupt changes in the membrane potential that sweep along the CELL MEMBRANE of excitable cells in response to excitation stimuli. Spike Potentials,Nerve Impulses,Action Potential,Impulse, Nerve,Impulses, Nerve,Nerve Impulse,Potential, Action,Potential, Spike,Potentials, Action,Potentials, Spike,Spike Potential
D000368 Aged A person 65 years of age or older. For a person older than 79 years, AGED, 80 AND OVER is available. Elderly
D000690 Amyotrophic Lateral Sclerosis A degenerative disorder affecting upper MOTOR NEURONS in the brain and lower motor neurons in the brain stem and SPINAL CORD. Disease onset is usually after the age of 50 and the process is usually fatal within 3 to 6 years. Clinical manifestations include progressive weakness, atrophy, FASCICULATION, hyperreflexia, DYSARTHRIA, dysphagia, and eventual paralysis of respiratory function. Pathologic features include the replacement of motor neurons with fibrous ASTROCYTES and atrophy of anterior SPINAL NERVE ROOTS and corticospinal tracts. (From Adams et al., Principles of Neurology, 6th ed, pp1089-94) ALS - Amyotrophic Lateral Sclerosis,Lou Gehrig Disease,Motor Neuron Disease, Amyotrophic Lateral Sclerosis,Amyotrophic Lateral Sclerosis With Dementia,Amyotrophic Lateral Sclerosis, Guam Form,Amyotrophic Lateral Sclerosis, Parkinsonism-Dementia Complex of Guam,Amyotrophic Lateral Sclerosis-Parkinsonism-Dementia Complex 1,Charcot Disease,Dementia With Amyotrophic Lateral Sclerosis,Gehrig's Disease,Guam Disease,Guam Form of Amyotrophic Lateral Sclerosis,Lou Gehrig's Disease,Lou-Gehrigs Disease,ALS Amyotrophic Lateral Sclerosis,Amyotrophic Lateral Sclerosis Parkinsonism Dementia Complex 1,Amyotrophic Lateral Sclerosis, Parkinsonism Dementia Complex of Guam,Disease, Guam,Disease, Lou-Gehrigs,Gehrig Disease,Gehrigs Disease,Sclerosis, Amyotrophic Lateral
D018485 Muscle Fibers, Skeletal Large, multinucleate single cells, either cylindrical or prismatic in shape, that form the basic unit of SKELETAL MUSCLE. They consist of MYOFIBRILS enclosed within and attached to the SARCOLEMMA. They are derived from the fusion of skeletal myoblasts (MYOBLASTS, SKELETAL) into a syncytium, followed by differentiation. Myocytes, Skeletal,Myotubes,Skeletal Myocytes,Skeletal Muscle Fibers,Fiber, Skeletal Muscle,Fibers, Skeletal Muscle,Muscle Fiber, Skeletal,Myocyte, Skeletal,Myotube,Skeletal Muscle Fiber,Skeletal Myocyte

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