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Assessment of Psychological Screeners for Spinal Cord Stimulation Success

Candidates for spinal cord stimulator implantation are typically referred for psychological assessment as part of the screening process to evaluate the likelihood of successful outcomes. The authors review the various assessment tools and discuss which may be most beneficial for chronic pain patients.
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Spinal cord stimulation (SCS) is a pain management strategy designed for patients with chronic pain (eg, neuropathic pain) that is refractory to medication and alternative or adjunct therapies, or who have experienced failed back surgery.1-3 The current literature suggests that psychological factors such as somatization, depression, anxiety, and poor coping are important predictors of poor outcome following SCS.4 Therefore, patients undergoing consideration for spinal cord stimulator implantation are typically referred for a psychological assessment as part of the process to determine their suitability and evaluate the likelihood of successful outcomes.5

For some clinicians, a brief interview may sufficiently screen for psychological factors, but in other cases, more extensive psychological testing is warranted.6 However, little information is available documenting either the role of such evaluations in categorizing potential candidates, or the utility of these assessments in predicting the likelihood of positive outcomes. Given the importance of psychological factors to treatment outcomes for a spinal cord stimulator implantation, we studied a population of patients referred for SCS-related psychological assessment to ascertain any patterns evident in their test scores. This paper reviews the results of our study.

Study Design

Eighty-six patients were identified as candidates for spinal cord stimulator implantation and underwent psychological assessments. All assessments were conducted by senior psychologists at Scott & White Healthcare/Texas A&M Health Science Center, which is located in the Central Texas region of the United States. Demographic measures (age, race/ethnicity, gender, marital status) and clinical data (prior and subsequent diagnoses, outpatient visits, and inpatient admissions) were collected from the electronic medical records and health plan data.

Psychological assessments included the following measures: Millon Behavioral Medicine Diagnostic (MBMD); Millon Clinical Multiaxial Inventory-3rd Edition (MCMI-III); Minnesota Multiphasic Personality Inventory-2nd Edition, Restructured Form (MMPI-2-RF); Shipley Institute of Living Scale (SILS); Beck Depression Inventory-II (BDI-II); and Beck Anxiety Inventory (BAI). The MBMD assesses negative health habits, psychiatric indications, coping styles, stress moderators, and treatment prognostics on scales of 0% to 100%.7 The MCMI-III assesses both acute syndromes and personality disorders, yielding scores of 0% to 100%; it was uniquely developed and normed on clinical populations.8,9 The MMPI-2-RF is a new version of the widely used MMPI-2, assessing a number of clinically relevant variables of one's emotional and personality functioning.10 The SILS assesses intellectual functioning and cognitive impairment with a self-administered 60-item instrument comprising 40 vocabulary test items and 20 items to assess abstract thinking.11 The BDI-II and BAI are self-administered checklists that assess symptoms of depression and anxiety.12,13

The analysis approach for this initial study was primarily descriptive, presenting an overall profile of this cohort of SCS candidates. Mean demographic characteristics, disclosure patterns, and summary scores for each instrument in the assessment battery were calculated, including means for each of the MBMD, MCMI-III, and MMPI-2-RF clinical subscales. Not all psychological instruments were administered to all candidates, based on the discretion of the clinician as well as the availability of tests at the time of assessment. The MBMD was administered to 79 out of the 86 participants within this sample; 62 participants completed the MCMI-III, and only 21 completed the MMPI-2-RF. The BDI-II was administered to 68 patients and the BAI was administered to 51 patients.

Study Results

Table 1 presents major findings from this study. The mean age of the sample was 52.7 years (range: 24 to 89 years), with the majority of participants being women (65.1%), white (74.4%), and married (66.6%). Participants' intellectual functioning was estimated by SILS to be in the average range (mean 99.5, SD 10.9). The mean BDI-II score denoted moderate levels of depressive symptoms (mean 20.0, SD 15.3), while average BAI scores also indicated moderate levels of anxiety (mean 16.6, SD 10.5).

Among MBMD response pattern scores, there was a notable percentage of response distortion for each of the validity scales, with about one-fifth (20.2%) of assessments showing at least a possible problem with negatively focused responding (Debasement), while more than one-quarter (27.9%) exhibited at least some possible problem with hesitation to disclose information in full (Disclosure). Nearly half (48.1%) of MBMD respondents showed possible or likely problems in their attempts to respond in a desirable manner (Desirability). In contrast, no elevations were noted for scales measuring response patterns on the MMPI-2-RF or MCMI-III. Since these two scales are primarily designed to detect psychopathology, the lack of noted elevations might not be an unusual finding.

The MBMD assesses the following health habits: alcohol, drugs, eating, caffeine, inactivity, and smoking. If a patient exhibited "likely" or "possible" problems for each habit, they were classified as having a negative behavior in that area. In this study, the most frequent problem areas observed among patients were overeating and inactivity. More than half (58.3%) of the participants had at least a possible issue with overeating, while close to two-thirds (68.4%) of participants indicated an issue with inactivity. About one-third (39.2%) of participants reported to have problems with smoking. Among MBMD clinical scales (denoted as prevalence rates or PR), several clinically significant elevations (ie, PR>75) were noted. These include the MBMD Stress Moderator scales for Illness Apprehension (mean 77.1, SD 13.4), Functional Deficits (mean 86.3, SD 14.1), and Pain Sensitivity (mean 97.0, SD 14.5). The MBMD Management Guides scale for Adjustment Difficulties also was elevated (mean 84.4, SD 11.3). This slight elevation would not be unusual for this population, given the patients' struggles with chronic pain. Also, this elevation would not necessarily prevent these patients from proceeding with the spinal cord stimulator implantation.

None of the MCMI-III scales were clinically elevated above the cutoff base rate score of 75. However, several mean scores for MMPI-2-RF clinical scales (presented as t-scores) were elevated above the clinical cutoff of 65. One elevated clinical scale denotes somatic complaints and preoccupation with health concerns (RC1: mean 68.3, SD 12.1). Other clinically significant mean scores were noted for sub-scale components of RC1, including malaise (mean 72.0, SD 11.0), head pain (mean 65.5, SD 10.8), and neurologicalcomplaints (mean 69.1, SD 13.7).

Last updated on: October 28, 2014
First published on: March 1, 2013