A 35-year-old man presented with exercise intolerance and muscle trembling since childhood. He was easily prone to fatigue and profuse sweating. Muscle trembling appeared during muscle forcing and disappeared during relaxation. Drinking alcohol could alleviate the tremble, and nervousness aggravated it. These symptoms did not progress or affect his daily life significantly for a long time. His 5-year-old daughter also presented almost the same symptoms.
On physical examination, his muscles trembled in high frequency during contraction. The upper arm trembled obviously when the arm lifted (Video), similar to engine vibration in palpation of the deltoid. The tremble likely originated from the contracted deltoid and further caused the trembling of surrounding tissue but did not cause joint movement. Other findings included bilateral deltoid (Medical Research Council Scale for Muscle Strength [MRC Muscle] grade 5-/5), biceps brachii (MRC Muscle grade 5-/5), and iliopsoas (MRC Muscle grade 4/5) weakness, mild hypomyotonia, and mild waddling gait. Cognition, sensation, cranial nerve functions, coordination assessment, tendon reflexes, and pathological signs were normal.
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Corresponding Author: Kunqian Ji, MD, Research Institute of Neuromuscular and Neurodegenerative Diseases and Department of Neurology, Qilu Hospital, Cheeloo College of Medicine, Shandong University, No. 107 West Wenhua Rd, Jinan, Shandong 250012, China (firstname.lastname@example.org).
Published Online: April 24, 2023. doi:10.1001/jamaneurol.2023.0818
Conflict of Interest Disclosures: This study was supported by grants from the National Key R&D Program of China (No. 2021YFC2700904), National Natural Science Foundation of China (No. 82171394), People’s Benefit Project of Science and Technology in Qingdao (16-6-2-1-nsh), and the Taishan Scholars Program of Shandong Province. No other disclosures were reported.
Additional Contributions: We thank the patient for granting permission to publish this information.
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