PROGNOSTIC VALUE OF PSYCHOLOGICAL-TESTING IN PATIENTS UNDERGOING SPINAL-CORD STIMULATION - A PROSPECTIVE-STUDY

OBJECTIVE: Associations between psychological and physical states are understood to exist, and the development of standardized psychological tests has allowed quantitative evaluation of this relationship. We te sted whether associations exist between psychological test instruments and patients selected for therapeutic trials of spinal cord stimulati on (SCS) for chronic, intractable pain. METHODS: Fifty-eight patients selected for SCS were tested prospectively with a battery of standardi zed psychological tests: Minnesota Multiphasic Personality Inventory w ith Wiggins content scales, Symptom Check List-90, and Derogatis Affec ts Balance Scale. Associations between treatment outcomes and preopera tive test scores and clinical variables were tested by univariate and multivariate statistical analyses, in which the dependent variables we re as follows: 1) the outcome of a therapeutic trial of stimulation (w hether the patient derived sufficient reported pain relief with a temp orary electrode to proceed with a permanent implant), and 2) long-term outcome of treatment with the permanent implant, as determined by dis interested third-party interview. RESULTS: Significant associations (P less than or equal to 0.01) were observed between the outcome of the therapeutic trial of stimulation and psychological test results; patie nts with low ''anxiety'' scores on the Derogatis Affects Balance Scale and with high ''organic symptoms'' scores on the Wiggins test were si gnificantly more likely to proceed to permanent implants, as determine d by multivariate statistical models. There was an elevation in the Mi nnesota Multiphasic Personality Inventory hypochondriasis scale in the se patients by univariate (P = 0.02), but not by multivariate, models. The multivariate model also identified young age, reproduction of leg pain by straight leg raising, and bilateral leg pain as favorable pro gnostic factors. The only association with favorable long-term outcome of implantation of a permanent device, by univariate analysis, was an elevated ''joy'' score on the Derogatis Affects Balance Scale. Multiv ariate analysis revealed no statistically significant predictors of lo ng-term outcome. CONCLUSION: Because our study population was selected on the basis of recognized prognostic factors and long clinical exper ience, it may not be possible to generalize our findings to the overal l pain clinic referral population. In the subpopulation we have chosen for SCS trials, psychological testing is of modest value and explains little of the observed variance in outcome. We find little evidence f or selecting patients for SCS on the basis of psychological testing. B ecause self-reported outcome measures may themselves reflect the patie nt's psychological state, these findings should be considered carefull y, in overall clinical context. A prospective study with additional ob jective outcome measures is underway, which will address some of these issues.