Images in Clinical Medicine
Percussion Myotonia
N Engl J Med 2009; 360:e13March 5, 2009
- Article
Video
Percussion Myotonia in Finger Extensors.
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, indicating myopathy. The creatine kinase level was 107 U per liter, and serum electrolytes were within the normal range. The patient had a history of hypercholesterolemia and cataracts and was receiving levothyroxine-replacement therapy after partial thyroidectomy for nodular disease; she had a normal thyroid level at the time of examination. There was no family history of any similar disorder. A molecular test detected a CTG triplet expansion in the dystrophia myotonica–protein kinase (DMPK) gene, confirming the diagnosis of type 1 myotonic dystrophy. Since the myotonia did not substantially reduce the patient's functioning, antimyotonic drugs were not recommended. At the last follow-up, 2 years after diagnosis, her muscle strength had deteriorated but she remained ambulatory.
Fabio A. Barroso, M.D.
Martin A. Nogues, M.D.
Raul Carrea Institute for Neurological Research, Buenos Aires 1428, Argentina
fbarroso@fleni.org. ar
