Objective: While integrity of spinal pathways below injury is generally thought to be an important factor in the success-rate of neuromodulation strategies for spinal cord injury (SCI), it is still unclear how the integrity of these pathways conveying the effects of stimulation should be assessed. In one of our institutional case series of five patients receiving dorsal root ganglion (DRG)-stimulation for elicitation of immediate motor response in motor complete SCI, only two out of five patients presented as responders, showing immediate muscle activation upon DRG-stimulation. The current study focuses on post hoc clinical-neurophysiological tests performed within this patient series to illustrate their use for prediction of spinal pathway integrity, and presumably, responder-status. Materials and Methods: In a series of three nonresponders and two responders (all male, American Spinal Injury Association [ASIA] impairment scale [AIS] A/B), a test-battery consisting of questionnaires, clinical measurements, as well as a series of neurophysiological measurements was performed less than eight months after participation in the initial study. Results: Nonresponders presented with a complete absence of spasticity and absence of leg reflexes. Additionally, nonresponders presented with close to no compound muscle action potentials (CMAPs) or Hofmann(H)-reflexes. In contrast, both responders presented with clear spasticity, elicitable leg reflexes, CMAPs, H-reflexes, and sensory nerve action potentials, although not always consistent for all tested muscles. Conclusions: Post hoc neurophysiological measurements were limited in clearly separating responders from nonresponders. Clinically, complete absence of spasticity-related complaints in the nonresponders was a distinguishing factor between responders and nonresponders in this case series, which mimics prior reports of epidural electrical stimulation, potentially illustrating similarities in mechanisms of action between the two techniques. However, the problem remains that explicit use and report of preinclusion clinical-neurophysiological measurements is missing in SCI literature. Identifying proper ways to assess these criteria might therefore be unnecessarily difficult, especially for nonestablished neuromodulation techniques.
|Number of pages||10|
|Publication status||Published - 1 Jun 2021|
Bibliographical noteFunding Information:
Frank J.P.M. Huygen is a member of the executive advisory board of Abbott and has received unrestricted educational grants from Saluda and Medtronic. In addition, he has received investigator‐initiated research grants from Spinal Modulation and St Jude (Abbott). Frank J.P.M. Huygen and Biswadjiet S. Harhangi hold a patent in relation to the present work (WO 2020/101485 A1). Chris I. De Zeeuw has received several research grants from the Medical NeuroDelta, LSH‐NWO Crossover INTENSE, and ZonMW. The other authors report no other financial conflicts of interest. Conflict of Interest:
The authors would like to express great gratitude to Marjan Scheltens-de Boer, Venny Pires, and Karla Biesheuvel at the Department of Clinical Neurophysiology of the Erasmus MC, for their role in the EMG-data acquisition. The authors would also like to thank Siri van der Meijden for her valuable support during measurements and initial data analysis.
© 2021 The Authors. Neuromodulation: Technology at the Neural Interface published by Wiley Periodicals LLC on behalf of International Neuromodulation Society.