Motor Unit Number Index (MUNIX): A novel neurophysiological marker for neuromuscular disorders; test–retest reliability in healthy volunteers

• Published in: Clinical neurophysiology Vol. 122; no. 9; pp. 1867 - 1872
• Main Authors: Neuwirth, Christoph, Nandedkar, Sanjeev, Stålberg, Erik, Barkhaus, Paul E., Carvalho, Mamede de, Furtula, Jasna, Dijk, Johannes P. van, Baldinger, Reto, Castro, José, Costa, João, Otto, Marit, Sandberg, Arne, Weber, Markus
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ireland Ltd 01.09.2011; Elsevier
• Subjects: Action Potentials - physiology; Adult; Aged; Aged, 80 and over; ALS; Biological and medical sciences; Diseases of striated muscles. Neuromuscular diseases; Electrodiagnosis. Electric activity recording; Electromyography - methods; Female; Humans; Investigative techniques, diagnostic techniques (general aspects); Male; Marker of disease progression; Medical sciences; MEDICIN; MEDICINE; Middle Aged; Motor Neurons - physiology; MUNE; MUNIX; Muscle, Skeletal - innervation; Nervous system; Neurology; Neuromuscular Diseases - diagnosis; Reproducibility of Results; Surface EMG; Test-retest reliability; Young Adult; BB; sMUP; EDB; CMAP; AH; ALS; ICC; Test–retest reliability; mV; ADM; ALSFRS-R; TA; MPS; MUNIX; SD; FVC; APB; DQEMG; Marker of disease progression; MUNE; SIP; EMG; MRC; Surface EMG; tibialis anterior muscle; surface-detected motor unit potentials; abductor digiti minimi muscle; forced vital capacity; motor unit number estimation; medical research counsil; revised amyotrophic lateral sclerosis functional rating scale; decomposition-based quantitative electromyography; amyotrophic lateral sclerosis; Motor Unit Number Index; surface interference pattern; abductor pollicis brevis muscle; extensor digitorum brevis muscle; intraclass correlation coefficient; multiple-point stimulation method; compound muscle action potential; millivolts; electromyography; biceps brachii muscle; abductor hallucis muscle; standard deviation; Test-retest reliability; Variability; Motor neuron disease; Electrophysiology; Action potential; Motor unit; Extensor digiti brevis muscle; Abductor pollicis brevis muscle; Degenerative disease; Correlation coefficient; Human; Nervous system diseases; Neuromuscular diseases; Test reliability; Abductor hallucis muscle; Abductor digiti minimi muscle; Striated muscle disease; Biceps brachii muscle; Central nervous system disease; Technique; Reliability; Spinal cord disease
• ISSN: 1388-2457; 1872-8952; 1872-8952
• DOI: 10.1016/j.clinph.2011.02.017

► Motor Unit Number Index (MUNIX) is a novel motor unit number estimation technique. ► It is non-invasive and fast to perform. ►This multicentre study tests intra- and inter-rater reliability in multiple muscles. ► A good reproducibility was shown in all muscles. To investigate the intra-rater and inter-rater test–retest reliability of the Motor Unit Number Index (MUNIX) in healthy subjects in a multicentre setting. Six study centres applied the MUNIX technique in 66 healthy subjects. Five to six muscles (biceps brachii, BB; abductor digiti minimi, ADM; abductor pollicis brevis, APB; tibialis anterior, TA; extensor digitorum brevis, EDB and abductor hallucis, AH) were measured in each volunteer four times by two independent examiners. The method was easy to perform and well tolerated. The intraclass correlation coefficient (ICC) varied between centres and muscles. Intra-rater reliability was greatest for the AH (ICC 0.83) and EDB (ICC 0.81). Inter-rater reliability was greatest for the AH (ICC 0.69) and ADM muscles (ICC 0.69). The most critical muscle was the APB muscle (ICC 0.52, total variability). This was mostly due to variability in the compound muscle action potential (CMAP) measurements. MUNIX values of the APB, ADM and TA fell into the same range as in other motor unit number estimation (MUNE) studies. MUNIX measurements in multiple muscles show good inter- and intra-rater reliability in healthy subjects. CMAP amplitude must be controlled to optimize reliability. Results suggest that MUNIX could serve as a reliable marker for motor neuron loss in diseases like amyotrophic lateral sclerosis.