BMI as a Predictor of Spinal Cord Stimulation Success in Chronic Pain Patients.

BACKGROUND: Spinal cord stimulation (SCS) is an effective method of treating chronic pain. Obese patients are overrepresented in chronic pain cases. We examine the effect of body mass index (BMI) on SCS success. METHODS: We prospectively follow outcome measures including visual analog score, Beck Depression Inventory (BDI), McGill Pain Questionnaire, Oswestry Disability Index (ODI), Pain Catastrophizing Scale (PCS), and the Insomnia Severity Index at baseline, six months, and one year postoperatively. Retrospectively, we examined whether our patients with a BMI above the 75th percentile (BMI ≥36.5) had worse outcomes. RESULTS: Our analysis included thoracic and cervical SCS patients-19 with a BMI ≥36.5 and 58 with a BMI <36.5. High BMI patients experienced less BDI improvement at 6 months (T(df) 2.257(36); p = 0.030; 95% CI [4.7%, 87.4%]) and one year (2.74(28); p = 0.011; 95% CI [18.1%, 125.0%]) post-SCS. High BMI patients had less improvement in pain as measured by the PCS at one year (U = 79.5; p = 0.045; 95% CI [-116.0%, 0.0%]). DISCUSSION: Each group experienced successful surgical outcomes. High BMI patients had less BDI improvement at six months and one year and less PCS improvement at one year. These data aid us in counseling our patients preoperatively.

A Single Center Prospective Observational Study of Outcomes With Tonic Cervical Spinal Cord Stimulation.

BACKGROUND: Spinal cord stimulation (SCS) has been a valuable resource for the treatment of chronic, nonmalignant pain that persists in the face of maximal medical management. A recent study demonstrated efficacy of cervical SCS in a multicenter registry. Here, in our single center study, we are able to delve into patient specifics, explore outcomes with percutaneous vs. paddle implants, and examine impact of patient symptomatology. METHODS: We prospectively collected data on subjects who underwent cervical SCS via numeric rating scale (NRS), McGill Pain Questionnaire, Oswestry Disability Index (ODI), and Beck Depression Inventory. Subjects completed this battery pre-operatively, at six months and at one year. Data were analyzed via repeated measures ANOVA, bivariate correlation analysis, and paired t-tests. RESULTS: In 30 consecutive subjects, 24 had a complete data set. The diagnosis was failed neck surgery syndrome (13%), Complex regional pain syndrome (29%), and neuropathic pain (58%). Compared with baseline, NRS score significantly improved at six months (p = 0.021) and one year (p = 0.047). ODI score also improved at one year (p = 0.009). At both six months and one year, subjects with percutaneous implants reported significantly less disability on ODI (p = 0.016 and 0.034, respectively), as compared with those who received paddle implants. There was no difference in NRS score or any other outcome measure based on type of implant. Diagnosis or region of pain did not correlate with any measure of outcome. DISCUSSION: We demonstrate that neck and arm pain can be improved with cervical SCS at six month and one-year follow-ups. Both percutaneous and paddle implants have benefit. We tend to place percutaneous implants for radicular pain and retrograde C1-2 paddles for axial pain that is ineffectively treated during the trial.

Effect of Eye Opening on Single-Unit Activity and Local Field Potentials in the Subthalamic Nucleus.

BACKGROUND: Subthalamic nucleus deep brain stimulation (STN DBS) is an established treatment in Parkinson's disease (PD). We investigate the effect of eye opening on neuronal activity and local field potentials (LFPs) in the STN. METHODS: We prospectively enrolled 25 PD patients undergoing STN DBS in our institution. During DBS, single-unit activity (SUA) and LFPs were measured when eyes were open and closed. As movement is known to result in changes in LFPs, we tested response to eye opening in the presence and absence of movement. RESULTS: Neither eye state nor arm movement has a significant influence on SUA recordings. There is a statistically significant interaction between eye state and arm movement (p < 0.05). In the presence of movement, STN SUA increase when eyes open (p < 0.05). When eyes are closed, STN SUA decrease with movement (p < 0.05). STN theta LFP oscillations decrease when eyes are open compared to closed, irrespective of movement status (p < 0.05). DISCUSSION: STN activity is influenced by eye state and arm movement. It is unclear whether this is attributed to a change in the STN's role in oculomotor control or from a change in attentional state. Understanding how physiologic normal activity alters neural activity is critical for the optimization of DBS therapy, particularly in closed-loop neuromodulation.

The Use of Preoperative Psychological Evaluations to Predict Spinal Cord Stimulation Success: Our Experience and a Review of the Literature.

BACKGROUND: Pre-operative psychological assessment is commonly used to assess patients for spinal cord stimulation (SCS). Though often times mandated by insurance, its value is frequently questioned. METHODS: We review the literature on the predictive value of psychological testing prior to SCS and retrospectively examine our prospective database of SCS patients. We examine associations of Minnesota Multiphasic Personality Inventory (MMPI), Beck Depression Inventory (BDI), and Pain Catastrophizing Scale (PCS) findings and outcomes on the visual analog scale (VAS), McGill Pain Questionnaire - Short Form (MPQ), and Oswestry Disability Index (ODI) at 6 and 12 months post-implantation. RESULTS: The nine studies examining psychological predictors of SCS outcomes collectively showed that substance abuse or feelings of demoralization or less joy correlated with worse outcomes. Though not statistically significant, our data show that at one year follow-up, patients without psychiatric disorders improved 1.5 times as much on ODI and 2.4 times as much on PCS as compared to patients with psychiatric disorders. Further, depressed patients concurrently treated with anti-depressants had greater improvement in BDI than non-medicated depressed patients (p = 0.009). We develop a tool for pain psychologists based on the existing literature to aid in identifying possible concerns and treating these patients peri-operatively. DISCUSSION: The predictive value of psychological testing depends on which psychiatric factors are used and which outcomes are measured. The predictive capacity of psychological indications can be used to holistically treat patients, specifically to recommend psychiatric medication and consulting to supplement SCS treatment as needed.

The Impact of Peripheral Nerve Stimulation on Disability and Depression.

BACKGROUND: Peripheral nerve stimulation (PNS) of the named nerves of the head has been shown to be effective in reducing pain levels in patients with chronic pain refractory to other treatments. However, the impact of cranial PNS on depression and disability has not been well documented. OBJECTIVES: We prospectively examine the impact of PNS on quality of life via validated survey scores which assess symptoms of depression and daily functional capacities within patients. METHODS: Patients who underwent permanent PNS implantation completed five validated questionnaires: Oswestry Disability Index (ODI), the Beck's Depression Inventory (BDI), the Pain Catastrophizing Scale (PCS), McGill Pain Questionnaire (MPQ), and the visual analog scale (VAS) score. These were completed at baseline, six months, and one year to assess changes in functioning levels. Results were analyzed via repeated measures ANOVA and bivariate analysis. RESULTS: Compared with baseline, at six months patients showed significantly less depression on BDI (F = 7.9, p = 0.021), and at one year, a significant decrease in disability was observed on the ODI (F = 6.1, p = 0.036). At both six months and one year, patients showed a significant decrease in pain on VAS (F = 16.5, p = 0.012). We noted a trend for ODI to correlate with BDI at six months (R = 0.616, p = 0.077). DISCUSSION: Our prospective data show PNS to be an effective modality in improving overall life quality by limiting depression and disability as well as pain.

A Prospective Study of the Intra- and Postoperative Efficacy of Intraoperative Neuromonitoring in Spinal Cord Stimulation.

BACKGROUND: Accurate lead placement is critical for spinal cord stimulation (SCS) efficacy. The traditional gold standard of awake placement is often technically difficult. While there is retrospective evidence supporting the use of intraoperative neurophysiological monitoring (IOM) as an alternative, a prospective assessment has not yet been performed. OBJECTIVE: To prospectively evaluate pain and functionality outcomes for IOM-guided SCS, validate two IOM modalities as a means to lateralize lead placement and assess whether IOM can be useful for postoperative programming. METHODS: A total of 73 patients were implanted with SCS using electromyography (EMG) and somatosensory-evoked potential collision studies (SSEP-CS) to verify lead placement. Patient pain and function were assessed through serial administration of several validated questionnaires. Stimulation parameters at 6 months were documented. RESULTS: Statistically significant (p < 0.05) improvements were observed in the McGill Pain Questionnaire, Oswestry Disability Index, Pain Catastrophizing Scale, and Visual Analog Scale. EMG and SSEP-CS appropriately lateralized leads in 65/73 (89.0%) and 40/58 (69.0%) cases, respectively. EMG predicted active contacts in use at follow-up with 82.7% sensitivity. CONCLUSIONS: We provide prospective evidence that IOM can be used to verify SCS placement. Additionally, EMG may help to streamline device programming and thereby improve outcomes by predicting the ideal stimulation contacts in many cases.

Predictors of Spinal Cord Stimulation Success.

INTRODUCTION: As many as 30% of spinal cord stimulation (SCS) patients fail to obtain long-term pain coverage, even with the strictest parameters of a successful trial, unremarkable psychological assessment, and ideal placement of the permanent device. Why these patients either never receive adequate benefit or lose benefit remains elusive. METHODS: We perform a retrospective review of our prospective database of SCS patients undergoing surgery for routine indications. Six-month postoperative follow-up data were available for 57 patients. Two providers who routinely saw the patients were asked to independently grade the patient's outcome in a blinded fashion on a Global Outcome Ratings scale of 1 to 10, with 5 being 50% improvement at 6 months postoperation. A score of less than 5 was deemed a failure. The impact of body mass index (BMI), random drug screen results, workers' compensation status, depression, and smoking were assessed. RESULTS: We report a phi correlation of 0.350 between smoking and failure (p = 0.017). Smoking status is correlated with both lead migration revisions (phi = 0.269) (p = 0.044) and with revision due to new pain symptoms (phi = 0.241) (p = 0.072). Further, there is a trend of correlation (phi = 0.289) between drug use and patients (N = 3) who underwent device removal (p = 0.045). In this cohort, worker's compensation status, BMI, and depression did not impact outcome. CONCLUSIONS: Tobacco use correlates with less success with SCS at 6-month follow-up. Whether that is because of issues with healing and our transmission of signals to the periphery warrants further exploration. These data provide further evidence that tobacco cessation is important to surgical results.

Clinical outcome and intraoperative neurophysiology for focal limb dystonic tremor without generalized dystonia treated with deep brain stimulation.

OBJECTIVES: Dystonic tremor (DT) is defined as a postural/kinetic tremor occurring in the body region affected by dystonia. DT is typically characterized by focal tremors with irregular amplitudes and variable frequencies typically below 7Hz. Pharmacological treatment is generally unsuccessful and guidelines for deep brain stimulation (DBS) targeting and indications are scarce. In this article, we present the outcome and neurophysiologic data of two patients with refractory, focal limb DT treated with Globus Pallidus interna (Gpi) DBS and critically review the current literature regarding surgical treatment of DT discussing stereotactic targets and treatment considerations. PATIENTS AND METHODS: A search of literature concerning treatment of DT was conducted. Additionally, Gpi DBS was performed in two patients with DT and microelectrode recordings for multi unit analysis (MUAs) and local field potentials (LFPs) were obtained. RESULTS: The mean percentage improvement in tremor severity was 80.5% at 3 years follow up. MUAs and LFPs did not show significant differences in DT patients compared with other forms of dystonia or PD except for higher interspikes bursting indices. LFP recordings in DT demonstrated high power at low frequencies with action (<3.5Hz). CONCLUSIONS: Gpi DBS is an effective treatment in patients with focal limb DT without associated generalized dystonia. Intraoperative neurophysiologic findings suggest that DT is part of phenotypic motor manifestations in dystonia.