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  • Title: The motor-evoked potentials elicited from the deltoid muscle by transcranial magnetic stimulation with a standardized facilitation: the potential diagnostic utility for C5 radiculopathy.
    Author: Inoue S, Tani T, Taniguchi S, Yamamoto H.
    Journal: Spine (Phila Pa 1976); 2003 Feb 01; 28(3):276-81. PubMed ID: 12567031.
    Abstract:
    STUDY DESIGN: We investigated the effects of standardized facilitation on stability in amplitude of the motor-evoked potentials from the deltoid muscle after magnetic stimulation over the scalp in normal study participants. OBJECTIVES: To test the potential of this technique in evaluating deltoid weakness and recovery after C5 radiculopathy. SUMMARY OF BACKGROUND DATA: Most previous motor-evoked potential studies have emphasized the value of the latency rather than amplitude, probably because the amplitude varies much more than the latency, even in the same individual. METHODS: Twenty right-handed healthy men underwent deltoid motor-evoked potential studies on three successive occasions at intervals of >2 weeks. A digital readout of the shoulder abduction force allowed the study participant to adjust voluntary contraction to 20% of the maximal force at the moment of stimulation. The deltoid motor-evoked potentials were compared with the M responses recorded from the relaxed deltoid after electrical stimulation of the brachial plexus. RESULTS: Despite considerable individual variability in the amplitude of deltoid motor-evoked potentials, a standardized facilitation yielded a relatively small variation of amplitude between sessions in the same individual, showing an intersession variability index of 9.1 +/- 7.9%. The side-to-side amplitude ratio, averaging 82 +/- 12%, also provides a more reliable measure in evaluating unilateral deltoid weakness than the absolute value. The measures on the left showed significantly higher amplitude than on the right for the deltoid motor-evoked potentials but not for the M responses. CONCLUSIONS: The changes of the motor-evoked potential amplitude exceeding 25% between sessions and side-to-side amplitude ratios <60% can be outside the normal limits. The asymmetry of deltoid motor-evoked potentials in favor of the nondominant side is of physiologic interest.
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