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Evoked Myotonia through Electrical Stimulation

Software is not in public domain. Procedure is in public domain.

Exploratory: Myotonic Dystrophy (DM)
Short Description of Instrument
The left arm of each subject was placed in an adjustable support with the left forearm secured to the armrest with Velcro wrap, the left elbow flexed at 90, forearm pronated, hand supported at the wrist, second digit secured in a ring clamp attached to a force transducer, and the thumb abducted and secured to an adjustable rod with paper tape. The ring force transducer was oriented horizontally and medially to the forearm, thus selectively measuring by compression of the load cell, the contraction force of index finger abduction. A bipolar surface bar electrode placed over the left ulnar nerve just proximal to the wrist was used to stimulate thenerve supramaximally. Each of the standardized trials consisted of one single stimulus trial, followed by five tetanic stimulus trials, each separated by a 10-min rest period. The tetanic trials were  in the following order: 10 stimuli at 10 HZ, 10 stimuli at 50 HZ, 10 stimuli at 30 HZ, 20 stimuli at 50 HZ, 20 stimuli at 30 HZ.

An automated computer program placed cursors along the declining (relaxation) phase of the force recordings at 90% and 5% of peak force (PF) and calculated relaxation times (RTs) between these points.

Comments/Special Instructions
Administration Time: 1 hour
Logigian EL, Twydell P, et al. (2010). Evoked myotonia can be "dialed-up" by increasing stimulus train length in myotonic dystrophy type 1. Muscle Nerve 41(2): 191-196.