Percussion Myotonia

A 60-year-old woman came to the hospital because of progressive gait difficulty. The physical examination revealed slight bilateral eyelid ptosis, temporalis muscle atrophy, and a waddling gait. Percussion of the finger extensor muscles and thenar eminence muscles evoked a myotonic phenomenon. A 60-year-old woman came to the neuromuscular clinic because of a progressive gait difficulty that had started insidiously 2 years before presentation. She could walk and climb stairs unassisted but with some difficulty. The physical examination revealed slight bilateral eyelid ptosis, temporalis muscle atrophy, and a waddling gait. Muscle strength was 4/5 in the scapular-girdle musculature and 3/5 in the hip flexors and extensors. Percussion of the finger extensor muscles and thenar eminence muscles evoked a myotonic phenomenon (figure and video). There was no grip myotonia. Sensation and coordination were preserved. Electromyography showed myotonic discharges and low-amplitude, short-duration motor-unit potentials, . . .