MOTOR UNIT NUMBER INDEX (MUNIX) IN THE ORBICULARIS OCULI MUSCLE OF HEALTHY SUBJECTS SUK-WON AHN, MD,1 KI-WON KIM, MT,2 JEE-EUN KIM, MD, PhD,3 JE-YOUNG SHIN, MD,2 DONG-GUN KIM, MD,2 KWANG-WOO LEE, MD, PhD,2 and JUNG-JOON SUNG, MD, PhD2 1

Department of Neurology, Chung-Ang University Hospital, Chung-Ang University College of Medicine, Seoul, Republic of Korea Department of Neurology, Seoul National University Hospital, Seoul National University College of Medicine, 28 Yongon-Dong, Chongno-gu, Seoul, 110-744, Korea 3 Department of Neurology, Seoul Medical Center, Seoul, Republic of Korea 2

Accepted 16 May 2014 ABSTRACT: Introduction: The motor unit number index (MUNIX) refers to an electrophysiological method that measures the number of motor units in the surface electromyographic interference pattern (SIP) recorded during graded muscle contractions. MUNIX studies of limb muscles have been conducted, but MUNIX studies of bulbo-facial muscles have not been reported. Methods: We assessed bilateral orbicularis oculi muscles using MUNIX, and the reference values and reproducibility of MUNIX and motor unit size index (MUSIX) were investigated in healthy subjects. Results: In this study, MUNIX was applied successfully to the orbicularis oculi muscles and showed good reproducibility. The correlation coefficients for MUNIX and MUSIX were 0.803 and 0.592, respectively, and the coefficients of variation were 20.9% and 8.5%, respectively. Conclusions: The MUNIX procedure for the orbicularis oculi muscle would be a useful tool for evaluating bulbar symptoms, especially in amyotrophic lateral sclerosis. Muscle Nerve 51: 197–200, 2015

The motor unit number index (MUNIX) was developed as an electrophysiological method for determining the functioning motor units that innervate a muscle or group of muscles.1–6 MUNIX is derived from the surface electromyographic interference pattern (SIP) recorded during voluntary contraction; this is performed instead of obtaining a mean surface motor unit potential, which is a critical element of motor unit number estimation (MUNE) techniques.3–9 MUNIX can significantly reduce patient discomfort and the duration of the test procedure as compared with MUNE. Although it is a brief test, MUNIX can provide valuable information regarding the number of motor units in a muscle and would be a practical electrophysiological method for assessing the progression of diseases such as amyotrophic lateral Abbreviations: ALS, amyotrophic lateral sclerosis; CMAP, compound muscle action potential; ICMUC, ideal case motor unit count; MUNE, motor unit number estimation; MUNIX, motor unit number index; MUSIX, motor unit size index; SIP, surface electromyographic interference pattern Key words: amyotrophic lateral sclerosis; facial nerve; motor unit; MUNIX; orbicularis oculi muscle This study was supported by grants from the Korea Healthcare Technology R&D Project, Ministry of Health and Welfare, Republic of Korea (HI09C10200200 and HI13C13340000), and the Basic Science Research Program through the National Research Foundation of Korea, funded by the Ministry of Science, ICT and Future Planning (2014R1A1A1005484). Correspondence to: J.-J. Sung; e-mail: [email protected] C 2014 Wiley Periodicals, Inc. V

Published online 28 May 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/mus.24292

MUNIX in Orbicularis Oculi Muscles

sclerosis (ALS). MUNIX software uses 5 different levels of isometric force to display voluntary surface electromyography (EMG) signals and, consequently, compute the results from the applicable muscles.3–6 Thus far, a few muscles, including abductor pollicis brevis (APB), abductor digiti minimi (ADM), biceps brachii (BB), tibialis anterior (TA), and abductor hallucis (AH), have been investigated.10 However, no MUNIX studies have assessed bulbo-facial muscles despite the fact that most ALS patients present with corticobulbar symptoms, including dysarthria, dysphagia, decreased tongue mobility, and facial weakness.11 Therefore, a MUNIX technique that can be used to assess such muscles would be valuable for evaluating progression in ALS. This study was performed to assess the orbicularis oculi muscle using the MUNIX technique; in addition, reference values and reproducibility of MUNIX in the orbicularis oculi muscle of healthy subjects were investigated. METHODS Subjects.

Healthy young adults were recruited consecutively from the Seoul National University Hospital, and the protocol was approved by the institutional review board. We excluded subjects who had a history of ocular injury, cerebral infarction or hemorrhage, diabetes, facial palsy, or peripheral neuropathy. We also excluded subjects who had abnormal clinical history or imaging studies or who had low-amplitude compound muscle action potentials in the orbicularis oculi (22

Motor unit number index (MUNIX) in the orbicularis oculi muscle of healthy subjects.

The motor unit number index (MUNIX) refers to an electrophysiological method that measures the number of motor units in the surface electromyographic ...
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