The Anterior Belly of the Digastric Muscle as a Novel Target for Needle Electromyography in Amyotrophic Lateral Sclerosis

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Abstract
Introduction/Aims: Needle electromyography (EMG) in the bulbar region aids in the diagnosis of amyotrophic lateral sclerosis (ALS) but remains technically challenging. The genioglossus muscle (GM) is commonly examined; however, pain and poor relaxation may limit its evaluation. The trapezius is an alternative target but is innervated by the spinal accessory nerve. We investigated the utility of the anterior belly of the digastric muscle (ABDM), innervated by the trigeminal nerve, for bulbar EMG evaluation. Methods: In this unblinded, prospective observational study, consecutive patients with suspected ALS underwent needle EMG of the ABDM, GM, masseter muscle (MM), and trapezius. Relaxation levels, EMG abnormalities, and pain (100‐mm visual analog scale [VAS]) were assessed. Results: Twenty‐seven clinically diagnosed ALS patients were analyzed. Relaxation was better in the ABDM than in the GM ( p < 0.001) and comparable to that in the MM and trapezius. Fasciculation potentials were detected more often in the ABDM (52%) than in the GM (0%) and MM (22%; p = 0.039) and were comparable to the trapezius (59%). Chronic denervation occurred at similar frequencies across muscles (33%–59%). The combination of abnormal spontaneous activity and chronic denervation was most frequent in the ABDM (37%). Pain was lower with the ABDM (median VAS score of 21) than with the GM (28; p = 0.0052) and MM (32; p < 0.001) and was similar to the trapezius (23). Discussion: The ABDM may be a practical additional target for bulbar EMG in ALS, with favorable relaxation, lower pain, and potentially improved electrodiagnostic yield.

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