How to Identify Responders and Nonresponders to Dorsal Root Ganglion-Stimulation Aimed at Eliciting Motor Responses in Chronic Spinal Cord Injury: Post Hoc Clinical and Neurophysiological Tests in a Case Series of Five Patients

Neuromodulation, 2021 · DOI: 10.1111/ner.13379 · Published: September 1, 2021

Simple Explanation

This study investigates why some patients with spinal cord injuries respond to dorsal root ganglion (DRG) stimulation, a technique to elicit motor responses, while others don't. Post-hoc clinical and neurophysiological tests were performed to identify factors that predict whether a patient will respond to DRG stimulation. The study found that the absence of spasticity and leg reflexes, along with the lack of compound muscle action potentials (CMAPs) or H-reflexes, were distinguishing factors in non-responders.

Study Duration

Less than eight months after participation in the initial study

Participants

Five patients with chronic motor complete SCI (American Spinal Injury Association [ASIA] impairment scale [AIS] A/B)

Evidence Level

Level 4: Case Series

Key Findings

1
Nonresponders presented with a complete absence of spasticity and absence of leg reﬂexes.
2
Nonresponders presented with close to no compound muscle action potentials (CMAPs) or Hofmann(H)-reﬂexes.
3
Responders presented with clear spasticity, elicitable leg reﬂexes, CMAPs, H-reﬂexes, and sensory nerve action potentials.

Research Summary

The study describes the post hoc clinical and neurophysiological assessment of five patients, three of whom were nonresponders in a neuromodulation study aimed at evoking motor response in motor complete SCI using bilateral L4-level DRG-stimulation. Nonresponders separated themselves from the responders in terms of absence of spasticity and absence of leg reﬂexes and presented with no CMAPs or H-reﬂexes. Complete absence of spasticity-related complaints in nonresponders was a distinguishing factor between responders and nonresponders, which mimics prior reports of EES, and perhaps warrants similar inclusion criteria for DRG-stimulation as EES.

Practical Implications

Patient Selection

Clinical assessments of spasticity and reflexes should be considered when selecting patients for DRG stimulation.

Treatment Strategies

Understanding the underlying mechanisms of DRG stimulation can help refine treatment strategies for SCI.

Future Research

Further research is needed to determine the best assessment tools for distinguishing between responders and nonresponders for DRG-stimulation, including MRI-analyses with or without neurological or neurophysiological assessments.

Study Limitations

1
The number of patients studied is very limited.
2
A more elaborate set of neurophysiological measurements involving more muscle groups, would be valuable in an experimental setting.
3
Measurements were performed up to eight months postcompletion of the initial study, which may have led to an inaccurate assumption of the status of our patients’ PNS during the initial study period.

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