This is any disorder involving tonic muscular spasm.
This may present as a clinical feature when the patient finds it difficult to unclasp his hand after shaking hands when greeting someone. It may be demonstrated formally by striking a muscle with a tendon hammer and watching the resultant "dimple" persist for a short time before filling up.
Conditions that cause myotonia include dystrophia myotonica.
Treatment - epanutin and procainamide are effective in reducing symptoms.
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