F98. Enhanced muscle evaluation using a novel impedance-electromyography (I-EMG) needle electrode

Abstract

Introduction A wealth of advantages has made needle electromyography (EMG) the standard, “go-to” clinical test used to evaluate muscle disorders. Nevertheless, EMG has associated technological limitations. For example, EMG only characterizes muscles’ active electrical activity, namely the depolarization of myofibers’ membrane. While clearly valuable, EMG does not provide information about non-electrically active (i.e. passive) properties altered in diseased muscle, the data’s being secondary to these alterations. One example of the relationship between passive and active electrical properties of muscle are the membrane resistance Rm (passive) and the membrane capacitance Cm (passive) of myofibers which determine the propagation velocity of action potentials (active). To date, measuring in vivo Rm, Cm and EMG using the same needle electrode was not possible. Methods We created a novel needle electrode integrating impedance and EMG technologies with the capability to measure simultaneously both passive (impedance) and active (EMG) electrical properties of muscle. We then conducted in vivo measurements in five C57BL/6 J wild-type mice at 6 weeks of age (The Jackson Lab, Bar Harbor, ME). Recordings were made in the gastrocnemius muscle with the animals mildly sedated (isoflurane 0.5–1% delivered by nosecone) while providing gentle stimuli to the hind limbs such that the animals repeatedly withdrew the limb. Results With our device, we were able to detect synchronized reductions in Rm and Cm with EMG activation. Rm is the inverse of the myofiber permeability; the higher the permeability, the lower Rm and vice versa. Cm is the ability of myofibers to store electrical charge. This result indicates the possibility to detect real-time passive and active electrical changes of myofibers during activity, which can provide additional information to help with the diagnosis. Conclusion Impedance technology embedded into an EMG needle electrode can greatly extend the diagnostic capabilities of needle EMG technology. Needle I-EMG could serve as a new bedside tool to assess muscle condition without increasing the complexity or duration of the standard needle EMG. Identifying changes in membrane properties of myofibers could serve as a convenient tool to assist with primary diagnosis or the impact of the therapies in a variety of conditions, including the denervating conditions and myotonic disorders.