Tremble of the Upper Arm and Ultrasonography of Deltoid Vibration in a Patient With an MYBPC1 Variant

A 35-year-old man presented with exercise intolerance and muscle trembling since childhood. Muscle trembling appeared during muscle contraction and disappeared during relaxation. B-mode ultrasonography showed irregular vibration of muscle bundles under contraction in both longitudinal and transverse sections of the deltoid muscle, while the subcutaneous tissue maintained a relative static state. Genetic testing revealed a pathogenic c.788T>G heterozygous variant in the MYBPC1 gene. To our knowledge, this is the first reported ultrasound image of the so-called myogenic tremor. The noninvasive dynamic visualization of muscle ultrasonography is helpful for its wider application in the differential diagnosis of neuromuscular diseases. Click the Related Article link for full details.