Patient-Specific Analysis of Neural Activation During Spinal Cord Stimulation for Pain.

OBJECTIVE: Despite the widespread use of spinal cord stimulation (SCS) for chronic pain management, its neuromodulatory effects remain poorly understood. Computational models provide a valuable tool to study SCS and its effects on axonal pathways within the spinal cord. However, these models must include sufficient detail to correlate model predictions with clinical effects, including patient-specific data. Therefore, the goal of this study was to investigate axonal activation at clinically relevant SCS parameters using a computer model that incorporated patient-specific anatomy and electrode locations. METHODS: We developed a patient-specific computer model for a patient undergoing SCS to treat chronic pain. This computer model consisted of two main components: 1) finite element model of the extracellular voltages generated by SCS and 2) multicompartment cable models of axons in the spinal cord. To determine the potential significance of a patient-specific approach, we also performed simulations with standard canonical models of SCS. We used the computer models to estimate axonal activation at clinically measured sensory, comfort, and discomfort thresholds. RESULTS: The patient-specific and canonical models predicted significantly different axonal activation. Relative to the canonical models, the patient-specific model predicted sensory threshold estimates that were more consistent with the corresponding clinical measurements. These results suggest that it is important to account for sources of interpatient variability (e.g., anatomy, electrode locations) in model-based analysis of SCS. CONCLUSIONS: This study demonstrates the potential for patient-specific computer models to quantitatively describe the axonal response to SCS and to address scientific questions related to clinical SCS.

Randomized clinical trial of deep brain stimulation for poststroke pain.

OBJECTIVE: The experience with deep brain stimulation (DBS) for pain is largely based on uncontrolled studies targeting the somatosensory pathways, with mixed results. We hypothesized that targeting limbic neural pathways would modulate the affective sphere of pain and alleviate suffering. METHODS: We conducted a prospective, double-blinded, randomized, placebo-controlled, crossover study of DBS targeting the ventral striatum/anterior limb of the internal capsule (VS/ALIC) in 10 patients with poststroke pain syndrome. One month after bilateral DBS, patients were randomized to active DBS or sham for 3 months, followed by crossover for another 3-month period. The primary endpoint was a ≥50% improvement on the Pain Disability Index in 50% of patients with active DBS compared to sham. This 6-month blinded phase was followed by an 18-month open stimulation phase. RESULTS: Nine participants completed randomization. Although this trial was negative for its primary and secondary endpoints, we did observe significant differences in multiple outcome measures related to the affective sphere of pain (eg, Montgomery-Åsberg Depression Rating Scale, Beck Depression Inventory, Affective Pain Rating Index of the Short-Form McGill Pain Questionnaire). Fourteen serious adverse events were recorded and resolved. INTERPRETATION: VS/ALIC DBS to modulate the affective sphere of pain represents a paradigm shift in chronic pain management. Although this exploratory study was negative for its primary endpoint, VS/ALIC DBS demonstrated an acceptable safety profile and statistically significant improvements on multiple outcome measures related to the affective sphere of pain. Therefore, we believe these results justify further work on neuromodulation therapies targeting the affective sphere of pain. Ann Neurol 2017;81:653-663.

Long-term outcomes after replacement of percutaneous leads with paddle leads in a retrospective cohort of patients with spinal cord stimulation systems.

BACKGROUND: Although the long-term outcomes for spinal cord stimulation (SCS) have been reported, long-term outcomes of patients who underwent revisions of the SCS with paddle leads are lacking. OBJECTIVE: To report the long-term outcomes of 39 patients who had percutaneous SCS revised with a new paddle lead. METHODS: Baseline and follow-up mail-in questionnaires assessed pain and disability levels with numerical rating scales, somatotopical overlap between SCS-related paresthesias and areas of chronic pain, and overall satisfaction. Analysis was performed with regard to age, sex, diagnosis, duration of disease, number of surgical revisions, complications, and interval between surgeries. RESULTS: After surgical revision, 20 patients (50%) had at least a 3-point reduction in the numerical rating scale. Greater pain reduction was correlated with better coverage (P = .001). Coverage area was greater in patients with a single revision than in patients with multiple revisions (P = .01). Good satisfaction was reported by 25 patients (62.5%) who indicated that they would undergo the procedure again in order to achieve the same results. These patients had significantly greater pain reduction (P = .001) and better coverage (P = .002) than patients who reported otherwise. No other major complication occurred. CONCLUSION: Revision of percutaneous SCS systems with implantation of a new paddle lead is safe and more effective in patients who have undergone not more than 1 prior revision.