Prognostic factors of spinal cord stimulation for chronic back and leg pain

Spinal cord stimulation (SCS) has been used for more than 20 years in the treatment of diverse pain conditions. Although recent studies have identified more clearly those conditions for which SCSoffers a favorable prognosis, the identification of a patient population in whom reasonably long-term success can be expected has been difficult. In an effort to improve patient selection and increase the overall success rate of treatment, we have examined various physical, demographic, and psychosocial variables as predictors of SCS outcome. The study population consisted of 40 patients with chronic low back and/or leg pain, 85% of whom were diagnosed with failed back surgery syndrome. Medical history and demographic data were collected as part of an initial assessment along with patient responses to the Minnesota Multiphasic Personality Inventory, the visual analogue pain rating scale (VAS), the McGill Pain Questionnaire, the Oswestry Disability Questionnaire, the Beck Depression Inventory, and the Sickness Impact Profile. Treatment outcomes were examined and found to improve significantly after 3 months of stimulation. Subsequent regression analysis revealed that patient age, the Minnesota Multiphasic Personality Inventory depression subscale D, and the evaluative subscale of the McGill Pain Questionnaire (MPQe) were important predictors of posttreatment pain status. Increased patient age and D subscale scores correlated negatively with pain status, as measured by the percentage of changes in pretreatment and posttreatment VAS scores, % delta VAS. In contrast, higher MPQe correlated with improved pain status. By the use of the following equation and the definition commonly associated with SCS success (at least 50% decrease in the VAS pain level), the success or failure of 3 months of SCS was correctly predicted in 88% of the study population. Our results suggest that patient age, Minnesota Multiphasic Personality Inventory depression, and MPQe may be clinically useful in the prediction of pain status after 3 months of SCS in patients with chronic low back and/or leg pain. % delta VAS = 112.57 - 1.98 (D)-1.68 (Age) + 35.54 (MPQe).