The association between pain intensity and disability in patients with failed back surgery syndrome, treated with spinal cord stimulation.

OBJECTIVE: Pain researchers demonstrated that pain intensity is not the most reliable measure of the success of chronic-pain treatment. Several research groups have proposed "core outcome domains", such as measurements of disability, to assess the effect of an intervention in pain patients. Up till now, studies investigating the relation between pain intensity and disability in patients treated with spinal cord stimulation (SCS) are lacking. Therefore, the current objective is to examine which pain-reporting strategy, routinely used in pain research, associates best with the degree of disability in these patients. METHODS: Eighty-one failed back surgery syndrome patients (37 males and 44 females, mean age 54.6 years), treated with high-dose spinal cord stimulation (HD-SCS) are recruited. Pain intensity was scored on an 11-point numerical rating scale (NRS) for leg and back pain, while disability was assessed with the Oswestry disability index (ODI). The association between both variables was investigated with Spearman's correlation and Cramér's V. RESULTS: Significant correlations (p < 0.001) are found between the absolute and relative differences of the ODI and NRS. Significant associations were found between reported cut-offs in literature (≤3, ≤5, and 50% pain relief) and the degree of disability. Finally, a significant association (p < 0.001) was found between the minimal clinical important difference. CONCLUSIONS: In this study, we showed that the degree of disability was strongly associated with the pain intensity as measured using different methods. The standard method for reporting pain intensity reduction (50%) seems to associate the strongest with the degree of disability. However, a low degree of disability does not always reflect a low pain intensity.Implications for rehabilitationThe degree of disability reveals a good association with the reporting methods of pain intensity from the literature.The Oswestry disability index could serve as a valid tool to measure the effect of spinal cord stimulation on pain.Disability measures offer a better insight in the clinical profile of chronic pain patients than a pain intensity score.

High-dose spinal cord stimulation for patients with failed back surgery syndrome: a multicenter effectiveness and prediction study.

ABSTRACT: The use of high-dose spinal cord stimulation (HD-SCS) has increased drastically during the past few years, with positive results. However, there remains a deficit of real-world data of the effectiveness of HD-SCS. Therefore, the primary aim was to evaluate the effectiveness of HD-SCS in patients with failed back surgery syndrome (FBSS). The second aim was to develop a prediction model for a holistic responder. One hundred ninety-four patients were recruited to a multicenter real-world registry. Self-reporting outcome variables were evaluated at baseline (before SCS) and at 1, 3, and 12 months of HD-SCS implant. Outcome measures were the mean pain intensity over time, sleep quality, disability, health-related quality of life, and medication use. Besides the effectiveness, logistic regression and decision tree analysis were performed to define a holistic responder (pain intensity reduction, medication reduction, Oswestry disability index reduction, and EQ5D improvement) after 12 months of HD-SCS. Of 185 FBSS patients who underwent a baseline visit, 75.13% had a successful HD trial. At 12 months, 92 patients were still receiving HD-SCS. Both low back and leg pain significantly decreased at 12 months. All outcome measures revealed a significant time-dependent effect from baseline to 12 months. Holistic responders could be predicted with a sensitivity and specificity of 90%. Clinically significant and sustained pain relief over a period of 12 months was achieved with HD-SCS in patients with FBSS. In addition, HD-SCS also achieved an improvement in sleep quality, functionality, and a decrease in pain medication.

The Long-Term Response to High-Dose Spinal Cord Stimulation in Patients With Failed Back Surgery Syndrome After Conversion From Standard Spinal Cord Stimulation: An Effectiveness and Prediction Study.

OBJECTIVES: Spinal cord stimulation (SCS) is nowadays available with several stimulation paradigms. New paradigms, such as high dose (HD-)SCS, have shown the possibility to salvage patients who lost their initial pain relief. The first aim of this study is to evaluate the effectiveness of HD-SCS after conversion from standard SCS. The second aim is to develop a model for prediction of long-term response of HD-SCS after unsatisfactory standard SCS. MATERIALS AND METHODS: Seventy-eight patients with failed back surgery syndrome (FBSS) who are treated with standard SCS were enrolled in the study. Self-reporting questionnaires and outcomes were assessed before conversion and at 1, 3, and 12 months of HD-SCS. Longitudinal mixed models were used to determine the effectiveness of HD-SCS. Logistic regression and classification and decision tree analyses were performed to predict responders (NRS decrease ≥2/10) after 12 months of HD-SCS. RESULTS: Significant time effects were found for both low back and leg pain responders, suggesting the effectiveness of HD-SCS after conversion. Logistic regression models revealed the importance of pain intensity scores, medication use, paresthesia coverage (for back pain) and EQ5D (for leg pain) as predictors for being a responder after 12 months of HD-SCS. CONCLUSIONS: Converting patients with unsatisfactory responses from standard SCS to HD-SCS may be an effective strategy to obtain and maintain pain relief in a challenging subgroup of patients with FBSS refractory to standard SCS. The prediction models may guide clinicians in their decision making when considering conversion to HD-SCS in patients with FBSS experiencing inadequate response to standard SCS.

The Added Value of High Dose Spinal Cord Stimulation in Patients with Failed Back Surgery Syndrome after Conversion from Standard Spinal Cord Stimulation.

Patients with Failed Back Surgery Syndrome (FBSS) report a considerably lower health- related quality of life (HRQoL), compared to the general population. Spinal cord stimulation (SCS) is an effective treatment to offer pain relief in those patients. Despite initial treatment success of SCS, its effect sometimes wears off over time. This study investigates the added value of high dose SCS (HD-SCS) in patients with unsatisfactory conventional SCS, from a quality of life perspective. Seventy-eight FBSS patients who were treated with conventional SCS that failed to provide pain relief, were recruited in 15 centers. HRQoL was assessed before converting to HD-SCS (baseline) and three times after converting to HD-SCS using the EuroQol-5D-3L. Quality adjusted life years (QALY) were calculated and compared with conventional SCS. An overall significant increase over time was seen in utility values of the EQ5D-3L, as the mean value at baseline 0.283 (±0.21) increased to 0.452 (±0.29) at 12 months of HD-SCS. This average increase in utility coincides with an average increase of 0.153 (±0.24) QALY's in comparison to continued conventional SCS. Besides the potential of HD-SCS to salvage patients with failed responses to conventional SCS, this treatment seems to be a more efficient treatment than conventional SCS.

Effects of spinal cord stimulation on voxel-based brain morphometry in patients with failed back surgery syndrome.

OBJECTIVE: Despite the clinical effectiveness of Spinal Cord Stimulation (SCS), potential structural brain modifications have not been explored. Our aim was to identify structural volumetric changes during subsensory SCS, in patients with Failed Back Surgery Syndrome (FBSS). METHODS: In this cohort study, twenty-two FBSS patients underwent a magnetic resonance imaging protocol before SCS and 3 months after SCS. Clinical parameters were correlated with volumetric changes, calculated with voxel-based morphometry. RESULTS: After 3 months, a significant volume decrease was found in the inferior frontal gyrus, precuneus, cerebellar posterior lobe and middle temporal gyrus. Significant increases were found in the inferior temporal gyrus, precentral gyrus and the middle frontal gyrus after SCS. Additionally, significant increases in volume of superior frontal and parietal white matter and a significant decrease in volume of white matter underlying the premotor/middle frontal gyrus were revealed after SCS. A significant correlation was highlighted between white matter volume underlying premotor/middle frontal gyrus and leg pain relief. CONCLUSIONS: This study revealed for the first time that SCS is able to induce volumetric changes in gray and white matter, suggesting the reversibility of brain alterations after chronic pain treatment. SIGNIFICANCE: Volumetric brain alterations are observable after 3 months of subsensory SCS in FBSS patients.

A Regions of Interest Voxel-Based Morphometry Study of the Human Brain During High-Frequency Spinal Cord Stimulation in Patients With Failed Back Surgery Syndrome.

INTRODUCTION: The effectiveness of spinal cord stimulation (SCS) as pain-relieving treatment for failed back surgery syndrome (FBSS) has already been demonstrated. However, potential structural and functional brain alterations resulting from subsensory SCS are less clear. The aim of this study was to test structural volumetric changes in a priori chosen regions of interest related to chronic pain after 1 month and 3 months of high-frequency SCS in patients with FBSS. METHODS: Eleven patients with FBSS who were scheduled for SCS device implantation were included in this study. All patients underwent a magnetic resonance imaging protocol before SCS device implantation 1 and 3 months after high-frequency SCS. Pain intensity, pain catastrophizing, and sleep quality were also measured. Regions-of-interest voxel-based morphometry was used to explore grey matter volumetric changes over time. Additionally, volumetric changes were correlated with changes in pain intensity, catastrophizing, and sleep quality. RESULTS: Significant decreases were found in volume in the left and right hippocampus over time. More specifically, a significant difference was revealed between volumes before SCS implantation and after 3 months of SCS. Repeated-measures correlations revealed a significant positive correlation between volumetric changes in the left hippocampus and changes in back pain score over time and between volumetric changes in the right hippocampus and changes in back pain score over time. CONCLUSION: In patients with FBSS, high-frequency SCS influences structural brain regions over time. The volume of the hippocampus was decreased bilaterally after 3 months of high-frequency SCS with a positive correlation with back pain intensity.

Magnetic Resonance Imaging Exploration of the Human Brain During 10 kHz Spinal Cord Stimulation for Failed Back Surgery Syndrome: A Resting State Functional Magnetic Resonance Imaging Study.

INTRODUCTION: Apart from the clinical efficacy of high frequency spinal cord stimulation at 10 kHz, the underlying mechanism of action remains unclear. In parallel with spinal or segmental theories, supraspinal hypotheses have been recently proposed. In order to unveil hidden altered brain connectome patterns, a resting state functional magnetic resonance imaging (rsfMRI) protocol was performed in subjects routinely treated for back and/or leg pain with high-frequency spinal cord stimulation (HF-SCS) HF-SCS at 10 kHz. METHODS: RsfMRI imaging was obtained from ten patients with failed back surgery syndrome who were eligible for HF-SCS at 10 kHz. Specifically-chosen regions of interest with different connectivity networks have been investigated over time. Baseline measurements were compared with measurements after 1 month and 3 months of HF-SCS at 10 kHz. Additionally, clinical parameters on pain intensity, central sensitization, pain catastrophizing, and sleep quality were correlated with the functional connectivity strengths. RESULTS: The study results demonstrate an increased connectivity over time between the anterior insula (affective salience network) and regions of the frontoparietal network and the central executive network. After 3 months of HF-SCS, the increased strength in functional connectivity between the left dorsolateral prefrontal cortex and the right anterior insula was significantly correlated with the minimum clinically important difference (MCID) value of the Pittsburgh sleep quality index. CONCLUSION: These findings support the hypothesis that HF-SCS at 10 kHz might influence the salience network and therefore also the emotional awareness of pain.

Association Between Spinal Cord Stimulation and Top-Down Nociceptive Inhibition in People With Failed Back Surgery Syndrome: A Cohort Study.

BACKGROUND: Descending nociceptive inhibitory pathways often malfunction in people with chronic pain. Conditioned pain modulation (CPM) is an experimental evaluation tool for assessing the functioning of these pathways. Spinal cord stimulation (SCS), a well-known treatment option for people with failed back surgery syndrome (FBSS), probably exerts its pain-relieving effect through a complex interplay of segmental and higher-order structures. OBJECTIVE: To the best of our knowledge, no clinical studies have thoroughly investigated the associations between SCS and CPM. DESIGN: This was a prospective cohort study in people with FBSS. METHODS: Seventeen people who had FBSS and were scheduled for SCS were enrolled in this study. The CPM model was evaluated at both sural nerves and was induced by electrical stimulation as the test stimulus and the cold pressor test as the conditioning stimulus. RESULTS: Before SCS, less than 30% of the participants with FBSS showed a CPM effect. Significant increases in the electrical detection threshold on the symptomatic side and the nonsymptomatic side were found. On the symptomatic side, no differences in the numbers of CPM responders before and after SCS could be found. On the nonsymptomatic side, more participants showed a CPM effect during SCS. Additionally, there were significant differences for CPM activation and SCS treatment. LIMITATIONS: Limitations were the small sample size and the subjective outcome parameters in the CPM model. CONCLUSIONS: This study revealed a bilateral effect of SCS that suggests the involvement of higher-order structures, such as the periaqueductal gray matter and rostroventromedial medulla (key regions in the descending pathways), as previously suggested by animal research.

Does Spinal Cord Stimulation Really Influence Sleep?

BACKGROUND: To date, clinical pain research has typically used subjective questionnaires to assess effectiveness of treatment. However, in the near future, new technologies may provide us objective outcome measures as an alternative to self-report. The goal of this study is to compare subjective and objective sleep assessments in a population of failed back surgery syndrome (FBSS) patients, treated with spinal cord stimulation (SCS). METHODS: Twenty-two patients diagnosed with FBSS received SCS. Sleep data was collected at three time point: prior to SCS implantation (B), one month after SCS (T1), and two months after SCS (T2). Sleep data measured by actigraphy provided objective sleep data and were compared to Pittsburgh sleep quality index (PSQI) scores. Agreement between sleep parameters, total sleep time (TST), sleep efficiency (SE), and sleep onset latency (SOL), was examined. RESULTS: Nineteen out of 22 patients completed the study. We identified significant differences between objective and subjective measurements for TST and SE at baseline and after two months of SCS, with patients underestimating both parameters on the PSQI in comparison to objective measurements. For SOL no significant differences were found, although patients subjectively overestimated SOL at B. CONCLUSION: The results about sleep measurements shown in this population of chronic pain patients, suggest that the subjective ratings scored worse than the objective measurements. Second, short-term SCS mainly seems to affect subjectively measured sleep parameters, especially SOL. This study shows the discrepancies between objective and subjective assessments in chronic pain research. Objective tools are indispensable for a correct assessment and treatment of sleep parameters. They are also playing a role as a biofeedback tool and are supporting the rehabilitation process.

Return to Work of Patients Treated With Spinal Cord Stimulation for Chronic Pain: A Systematic Review and Meta-Analysis.

BACKGROUND: Chronic pain has a substantial negative impact on work-related outcomes, which underscores the importance of interventions to reduce the burden. Spinal cord stimulation (SCS) efficiently causes pain relief in specific chronic pain syndromes. The aim of this review was to identify and summarize evidence on returning to work in patients with chronic pain treated with SCS. MATERIALS AND METHODS: A systematic literature review was performed including studies from PubMed, EMBASE, SCOPUS, and Web of Science (up till October 2017). Risk of bias was assessed using a modified version of the Downs & Black checklist. Where possible, we pooled data using random effects meta-analysis. The study protocol was registered prior to initiation of the review process (PROSPERO CRD42017077803). RESULTS: Fifteen full-text articles (total articles screened: 2835) were included. Risk of bias for these articles was scored low. Seven trials provided sufficient data and were judged similar enough to be pooled for meta-analysis on binary outcomes. SCS intervention results in a higher prevalence of patients at work compared with before treatment (odds ratio [OR] 2.15; 95% confidence interval [CI], 1.44-3.21; I2 = 42%; p < 0.001). SCS treatment also results in high odds to return to work (OR 29.06; 95% CI, 9.73-86.75; I2 = 0%; p < 0.001). CONCLUSIONS: Based on available literature, SCS proved to be an effective approach to stimulate return to work in patients with specific chronic pain syndromes.

Functional magnetic resonance imaging: cerebral function alterations in subthreshold and suprathreshold spinal cord stimulation.

BACKGROUND AND PURPOSE: Failed back surgery syndrome (FBSS) is a common and devastating chronic neuropathic pain disorder. Conventional spinal cord stimulation (SCS) applies electrical suprathreshold pulses to the spinal cord at a frequency of 40-60 Hz and relieves pain in FBSS patients. During the last decade, two major changes have emerged in the techniques of stimulating the spinal cord: paresthesia-free or subthreshold stimulation and administration of higher frequency or higher amounts of energy to the spinal cord. Despite the positive clinical results, the mechanism of action remains unclear. A functional MRI (fMRI) study was conducted to investigate the brain alterations during subthreshold and suprathreshold stimulation at different frequencies. METHODS: Ten subjects with FBSS, treated with externalized SCS, received randomly four different stimulation frequencies (4 Hz, 60 Hz, 500 Hz, and 1 kHz) during four consecutive days. At every frequency, the patient underwent sub- and suprathreshold stimulation. Cerebral activity was monitored and assessed using fMRI. RESULTS: Suprathreshold stimulation is generally accompanied with more activity than sub-threshold SCS. Suprathreshold SCS resulted in increased bilateral activation of the frontal cortex, thalamus, pre- and postcentral gyri, basal ganglia, cingulate gyrus, insula, thalamus, and claustrum. We observed deactivation of the bilateral parahippocampus, amygdala, precuneus, posterior cingulate gyrus, postcentral gyrus, and unilateral superior temporal gyrus. CONCLUSION: Suprathreshold stimulation resulted in greater activity (both activation and deactivation) of the frontal brain regions; the sensory, limbic, and motor cortices; and the diencephalon in comparison with subthreshold stimulation. Each type of frequency at suprathreshold stimulation was characterized by an individual activation pattern.

Cerebral Biochemical Effect of Pregabalin in Patients with Painful Diabetic Neuropathy: A Randomized Controlled Trial.

INTRODUCTION: With the development of new neuroimaging tools it has become possible to assess neurochemical alterations in patients experiencing chronic pain and to determine how these factors change during pharmacological treatment. The goal of this study was to examine the exact neurochemical mechanism underlying pregabalin treatment, utilizing magnetic resonance spectroscopy (1H-MRS), in a population of patients with painful diabetic polyneuropathy (PDN), with the overall aim to ultimately objectify the clinical effect of pregabalin. METHODS: A double blind, randomized, placebo-controlled study was conducted. A total of 27 patients with PDN were enrolled in the study, of whom 13 received placebo treatment (control group) and 14 received pregabalin (intervention group). Pregabalin treatment consisted of stepwise dose escalation over the study period from 75 mg daily ultimately to 600 mg daily. 1H-MRS was performed at 3T on four regions of interest in the brain: the rostral anterior cingulate cortex (rACC), left and right thalamus and prefrontal cortex. The absolute concentrations of N-acetyl aspartate, glutamate, glutamine, gamma-amino-butyric-acid (GABA), glucose (Glc) and myo-inositol (mINS) were determined using LCModel. RESULTS: The concentration of most neurometabolites in the placebo and pregabalin group did not significantly differ over time, with only a small significant difference in Glc level in the left thalamus (p = 0.049). Comparison of the effects of the different doses revealed significant differences for mINS in the rACC (baseline 2.42 ± 1.21 vs. 450 mg 1.58 ± 0.94; p = 0.022) and dorsolateral prefrontal cortex (75 mg 2.38 ± 0.89 vs. 450 mg 1.59 ± 0.85; p = 0.042) and also for GABA in the rACC (75 mg 0.53 ± 0.51 vs. 225 mg 0.28 ± 0.19; p = 0.014). CONCLUSION: No differences were found in metabolite concentrations between the placebo (control) and intervention groups, but some differences, although small, were found between the different doses. TRIAL REGISTRATION: This study is registered at ClinicalTrials.gov (NCT01180608). FUNDING: Lyrica Independent Investigator Research Award (LIIRA) 2010 (Pfizer) funded the study.

Return to work following surgery for lumbar radiculopathy: a systematic review.

BACKGROUND CONTEXT: Informing patients about postoperative return to work (RTW) expectations is of utmost importance because of the influence of realistic expectations on RTW outcomes. PURPOSE: We aimed to give an overview of the duration of sick leave and RTW rates after surgery for lumbar radiculopathy and to list predictors of and factors related to RTW. STUDY DESIGN: A systematic review was carried out. METHODS: A systematic literature search was conducted in PubMed, Web of Science, EMBASE, and SCOPUS. Full-text articles on RTW following surgery for lumbar radiculopathy were included through double-blind screening. Risk of bias was assessed using a modified version of the Downs and Black checklist. RESULTS: Sixty-three full-text articles (total sample size: 7,100 patients) were included. Risk of bias was scored low to high. Mean duration of sick leave ranged from 0.8 to 20 weeks. Within 0.1-240 months post surgery, 3%-100% of patients resumed work. Most important predictors for work resumption were preoperative work status, presence of comorbidities, age, sex and duration of preoperative symptoms. Duration of sick leave can be predicted by the preoperative level of pain or disability and presence of symptoms of depression, occupational mental stress, and lateral disc prolapse. Furthermore, less invasive surgical techniques were found to result in better RTW outcomes compared with more invasive techniques. CONCLUSIONS: Diverse results were found for RTW rates and duration of sick leave. Preoperative work status, presence of comorbidities, and several demographic factors were retrieved as predictors of RTW and duration of sick leave.

Is the Self-Reporting of Failed Back Surgery Syndrome Patients Treated With Spinal Cord Stimulation in Line With Objective Measurements?

OBJECTIVES: To understand the subjective pain experience of patients, healthcare providers rely heavily on self-reporting. However, to quantify this unique pain experience, objective parameters are not yet available in daily clinical practice. With regard to patients with failed back surgery syndrome (FBSS) treated with spinal cord stimulation (SCS), pain therapists may recover the individual functional information about the patient's posture from the implantable pulse generator (IPG) of the stimulator. The aim of this study is to investigate whether subjective self-reporting is in correlation with the functional capacities of a patient. MATERIALS AND METHODS: Thirty-nine patients with FBSS, treated with SCS were included. The accelerometer in the IPG detects positional changes and provides an objective output of seven functional positions (lying back, lying prone, lying left, lying right, transition, upright, and upright + mobile). The Oswestry Disability Index (ODI), VAS-diary, and the Pittsburgh Sleep Quality Index (PSQI) were assessed to evaluate physical functioning, pain intensities, and subjective sleep quality. Additionally, 21 patients wore a wearable actigraph device to objectify sleep quality. The agreement and Spearman correlations between objective and subjective parameters were assessed. RESULTS: Spearman rank correlations revealed no significant correlations between the ODI (subscales walking, sitting, standing, and sleeping) and the output of the IPG (percentage upright + mobile, transition, upright, and lying, respectively). Sleep parameters measured with the Actiwatch and the PSQI were not in agreement. CONCLUSIONS: This study demonstrated that self-reporting questionnaires do not correlate with the findings of objective measurements. Therefore, we recommend using both subjective and objective parameters when determining treatment options for FBSS patients.

One single bout of low-intensity isometric handgrip exercise reduces blood pressure in healthy pre- and hypertensive individuals.

BACKGROUND: The aim of this study was to investigate the acute effect of one single session of isometric handgrip exercise (IHG) on blood pressure (BP) during daily life activities in healthy adults. METHODS: Fifteen healthy adults with pre- or stage 1 hypertension (10 men; mean age 48±7.1 years) completed two experimental sessions in random order: one control (rest for 15 minutes) and one low intensity IHG session (4×2 minutes sustained contractions at 30% of maximal volutional contraction interspersed with 1-minute rest intervals). Blood pressure was recorded before each intervention and following the intervention BP was recorded for one hour in the office and thereafter for 6 hours during their daily activities by means of an ambulatory BP device. Physical activity (number of steps and total energy expenditure) was assessed by means of a SenseWear mini device. RESULTS: Systolic BP was higher the first minute after the isometric handgrip exercise but quickly returned to baseline levels after 15 minutes in the office. Over the 7-hour period, systolic blood pressure was significantly lower (-5.4±7.3 vs. +0.23±6.9; P<0.05) after IHG compared to the control session. Although not significant, a tendency was observed towards a lower diastolic blood pressure after IHG compared to control (P=0.09). Physical activity behavior was similar on both days (P>0.05). CONCLUSIONS: This study demonstrates that one single bout of IHG can result in an overall reduction in BP during daily activities. More research is needed to confirm these findings and to explain possible mechanisms responsible for these observed changes.

High-Density in Spinal Cord stimulation: Virtual Expert Registry (DISCOVER): Study Protocol for a Prospective Observational Trial.

BACKGROUND: Spinal cord stimulation (SCS) is a proven and effective treatment for neuropathic pain conditions such as failed back surgery syndrome (FBSS). The hypothesis that different settings for SCS parameters activate unique, pain-relieving mechanisms has boosted the development of various SCS paradigms. High density spinal cord stimulation (HD-SCS) is one of those promising, novel stimulation forms characterized by subthreshold stimulation, delivering more pulses per second and a higher pulse density to the spinal cord than conventional SCS. OBJECTIVES: The aim of DISCOVER is to gather evidence about the effectiveness, feasibility, and (possible) side effects of HD stimulation. METHODS: The prospective, non-interventional, multi-center, clinical study, DISCOVER, is currently restricted to Belgium where 19 neuromodulation centers were selected. Patient recruitment started in October 2016 and is expected to end in October 2017. Subjects included are (1) patients with insufficient pain relief from conventional SCS or (2) neurostimulation-naïve patients suited for SCS. Patients will be assessed 1 month, 3 months, and 12 months after conversion to HD-SCS settings. Each patient's visit will include: a numerical rating scale (NRS), Oswestry disability index (ODI), Pittsburgh sleep quality index (PSQI), EQ-5D, a pain map, registration of SCS settings, and a list of used pain medication. CONCLUSIONS: Although promising results have been reported, adequate registration of its effectiveness and (possible) side-effects remains an unmet need. Main results are expected in 2019.