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A 39-year-old woman presented with a 2-year history of distal lower limbs muscle weakness and bilateral finger stiffness without pain. She reported of inability to stand on her toes and relax the fingers after squeezing her hands. The symptom improved with repeated movements. The patient did not have a family history of any dystrophic myotonic syndrome. On neurological examination, the relaxation of fingers was delay after griping (grip myotonia, figures 1 and 2, and video 1) and bilateral gastrocnemius muscle weakness. Laboratory test revealed elevated creatine kinase (435 U/L) and aldolase (11.8 U/L). MRI of the lower limbs showed bilateral gastrocnemius muscles atrophy (figure 3). The electromyogram revealed complex repetitive discharges and myotonic discharge. Dystrophia myotonica protein kinase gene testing showed a cytosine-thymine-guanine (CTG) repeat expansion of 200 (normal value <35), and myotonic dystrophy type 1 (DM1) was diagnosed.
DM1 is an adult-onset muscular dystrophy that is an autosomal dominant myopathic CTG triplet disorder.1 DM1 presents slowly progressive face, neck and distal muscle weakness.2 Delayed grip release after handshaking or screwing on the cap is often a helpful clue to diagnose the disease. Repeated use of the muscle can reduce the stiffness. This is known as ‘warm-up’ phenomenon.3 The former sign is only seen in the early stage of DM1 and disappears as the disease progresses to develop muscle atrophy.4
Myotonic dystrophy type 1 presents slowly progressive face, neck and distal muscle weakness.
Grip myotonia is a characteristic sign even in the early stages of myotonic dystrophy type 1.
Contributors YY and KS managed the patient. YY and KS wrote the first draft. MI revised the manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
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