Is Life Better After Motor Cortex Stimulation for Pain Control? Results at Long-Term and their Prediction by Preoperative rTMS

Abstract

Background: A positive effect of motor cortex stimulation (MCS) (defined as subjective estimations of pain relief ≥ 30%) has been reported in 55 – 64% of patients. Repetitive magnetic cortical stimulation (rTMS) is considered a predictor of MCS effect. These figures are, however, mostly based on subjective reports of pain intensity, and have not been confirmed in the long-term. Objectives: This study assessed long-term pain relief (2 – 9 years) after epidural motor cortex stimulation and its pre-operative prediction by rTMS, using both intensity and Quality of Life (QoL) scales. Study Design: Analysis of the long-term evolution of pain patients treated by epidural motor cortex stimulation, and predictive value of preoperative response to rTMS. Setting: University Neurological Hospital Pain Center. Methods: Patients: Twenty patients suffering chronic pharmaco-resistant neuropathic pain. Intervention: All patients received first randomized sham vs. active 20Hz-rTMS, before being submitted to MCS surgery. Measurement: Postoperative pain relief was evaluated at 6 months and then up to 9 years post-MCS (average 6.1 ± 2.6 y) using (i) pain numerical rating scores (NRS); (ii) a combined assessment (CPA) including NRS, drug intake, and subjective quality of life; and (iii) a short questionnaire (HowRu) exploring discomfort, distress, disability, and dependence. Results: Pain scores were significantly reduced by active (but not sham) rTMS and by subsequent MCS. Ten out of 20 patients kept a long-term benefit from MCS, both on raw pain scores and on CPA. The CPA results were strictly comparable when obtained by the surgeon or by a third-party on telephonic survey (r = 0.9). CPA scores following rTMS and long-term MCS were significantly associated (Fisher P = 0.02), with 90% positive predictive value and 67% negative predictive value of preoperative rTMS over long-term MCS results. On the HowRu questionnaire, long-term MCSrelated improvement concerned “discomfort” (physical pain) and “dependence” (autonomy for daily activities), whereas “disability” (work, home, and leisure activities) and “distress” (anxiety, stress, depression) did not significantly improve. Limitations: Limited cohort of patients with inhomogeneous pain etiology. Subjectivity of the reported items by the patient after a variable and long delay after surgery. Predictive evaluation based on a single rTMS session compared to chronic MCS. Conclusions: Half of the patients still retain a significant benefit after 2 – 9 years of continuous MCS, and this can be reasonably predicted by preoperative rTMS. Adding drug intake and QoL estimates to raw pain scores allows a more realistic assessment of long-term benefits and enhance the rTMS predictive value. The aims of this study and its design were approved by the local ethics committee (University Hospitals St Etienne and Lyon, France). Key words: Neuropathic pain, chronic refractory pain, repetitive transcranial magnetic stimulation, rTMS, epidural motor cortex stimulation, MCS, quality of life, predictive value