Reference data for quantitative motor unit potential analysis in the genioglossus muscle

REFERENCE DATA FOR QUANTITATIVE MOTOR UNIT POTENTIAL ANALYSIS IN THE GENIOGLOSSUS MUSCLE Needle electromyography (EMG) of the genioglossus muscle is a potentially useful investigation in patients with speech or swallowing problems in whom a neuromuscular disorder (e.g., amyotrophic lateral sclerosis [ALS], hypoglossal neuropathy) is suspected, as well as in patients with subclinical bulbar involvement (e.g., ALS).3 Although template operated multi-MUP (motor unit potential) analysis is clinically much more useful than older techniques, until now no appropriate reference data for MUPs have been published for this muscle. The aim of the present study was, therefore, to establish reference intervals for MUP parameters using template operated multi-MUP analysis in the genioglossus muscle. We studied 20 healthy volunteers (11 men, 9 women), 24–55 years old (mean, 38 years) with no speech or swallowing problems or neuromuscular disorder. The study was approved by the National Ethics Committee of Slovenia, and all subjects provided informed consent. Standard disposable concentric EMG needles with a recording area of 0.07 mm, and an EMG system (Keypoint, Alpine Biomed Neurodiagnostics, Skovlunde, Denmark) with standard settings (filters: 5 Hz – 10 kHz) were used. Needle electrodes were inserted 2–3 cm from the tip of the chin and 1 cm medial to the mandible (i.e., using an inframandibular approach).2 After obtaining a sharp EMG signal the needle electrode was inserted 1 cm deeper before sampling of MUPs was commenced using multi-MUP analysis.7 To reduce too high muscle activity during MUP sampling we examined subjects in a supine position. For each MUP parameter (Table 1) upper and lower normative limits for mean values (mean 2 SD), and outlier limits (the 5th percentile of the third lowest and the 95th percentile of the third highest values) were calculated from the first 20 sampled MUPs.4,6 In each of 20 subjects at least 20 MUPs were obtained. Duration cursors were not changed; MUPs with an unsteady baseline were deleted. Student’s t-test for unpaired samples was used to compare the mean values obtained in the biceps brachii and genioglossus muscles. Normative data for individual MUP parameters and their relation to biceps brachii muscle are presented in Table 1. The present study provides quantitative measures of genioglossus muscle MUPs using the template operated multi-MUP analysis technique. Previously, only data for amplitude (224 48.7 mV) and duration (6.6 0.75 ms) obtained by single MUP analysis have been published.3 The higher amplitudes and shorter durations found in our study might be explained by: (1) differences between the tongue muscle inserted through the mouth3 and the genioglossus muscle using the submandibular approach; (2) the use of different MUP sampling techniques.3 We found most MUP parameters obtained in the genioglossus muscle to be smaller compared to those in a typical limb muscle (e.g., biceps brachii; Table 1). This finding might be explained by smaller (25–30 m5) muscle fiber diameters in the genioglossus muscle compared to typical limb muscle (e.g., biceps brachii, 60 m1).8 Other data that might also contribute to observed differences in MUP parameters (i.e., muscle fiber densities and lengths)8 is to our knowledge not available for the genioglossus muscle.