Introduction: Chronic back pain (CBP) has been associated with alterations in functional connectivity (FC) but data is limited and based on heterogeneous populations.[1-5] Based on our previous work, we hypothesize that FBSS patients have altered FC across networks involving emotion and reward/aversion functions, and that these changes may be correlated with spinal cord stimulation (SCS) outcomes.
Methods: Five, non-pregnant, adult FBSS patients with implanted SCS systems (Medtronic) were enrolled. All imaging protocols were approved by our MRI Safety committee. Anatomical and resting state (RS) fcMRIs were obtained during two separate visits. The subjects underwent off-and-on testing with non-bursting and bursting SCS at visits 1 and 2, respectively. Patient surveys were administered before and after SCS. Outcome measures focused on FC patterns, STM-index, and pain scales.
Results: FcMRI sequences were safely acquired for all patients with implanted SCS systems using 3T-MRI. Off-and-on testing of non-bursting stimulation resulted in a significant decrease of STM indices when non-bursting SCS was restored (mean STM-index 0.25 vs 0.13, p=0.006). No significant difference was seen in STM indices during on-and-off testing of bursting stimulation (mean STM-index 0.20 vs 0.19, p=0.67). The bursting pattern was preferred by 4 of 5 patients. All reported pain scores decreased during on testing. Pain catastrophizing scores (PCS) were significantly lower after switching from non-bursting to bursting pattern stimulation (mean PCS 17.6 vs 14.6, p=0.02).
Conclusions: Preliminary results suggest there is no correlation between the instantaneous pain scores and STM-index for patients with implanted therapeutic SCS systems which contrasts with findings from our previous study in FBSS patients after a successful SCS trial. STM indices for SCS-treated FBSS patients appeared to cluster around the normal levels seen in control non-FBSS patients. The STM-index may represent a biomarker specific to FBSS patients, which may help guide patient selection for SCS and treatment optimization.
Patient Care: Characterization of a pain biomarker specific to the neuropathic pain phenotype seen in FBSS, may help guide patient selection for SCS as well as treatment optimization (e.g. tonic vs bursting stimulation patterns).
Learning Objectives: By the conclusion of this session, participants should be able to:
1. Describe the role of functional connectivity MRI in the study of chronic pain syndromes.
2. Describe current challenges in the management of patients with chronic pain, specifically those with failed back surgery syndrome (FBSS).
3. Describe the concept of pain biomarkers and their potential to guide patient selection for spinal cord stimulation (SCS) as well as treatment optimization.
4. Describe the differences between bursting vs non-bursting stimulation patterns in SCS
References: 1. Baliki, M. N., A. R. Mansour, A. T. Baria and A. V. Apkarian (2014). "Functional reorganization of the default mode network across chronic pain conditions." PLoS One 9(9): e106133.
2. Baliki MN, Apkarian AV. (2015). Nociception, pain, negative moods and behavior selection. Neuron 87 (3): 474-491.
3. Baliki MN, Petre B, Torbey S, Herrmann KM, Huang L, Schnitzer TJ, Fields HL, Apkarian AV. (2012). Corticostriatal functional connectivity predicts transition to chronic back pain. Nature Neurosci 15 (8): 1117-1119.
4. Hashmi JA, Baliki M, Huang L, Baria AT, Torbey S, Hermann KM, Schnitzer TJ, Apkarian AV. (2013). Shape shifting pain: chronification of back pain shifts brain representation from nociceptive to emotional circuits. Brain 136: 2571-2768.
5. Yu, R, Gollub RL, Spaeth R, Napadow V, Wasan A, Konga J. (2014). Disrupted functional connectivity of the periaqueductal gray in chronic low back pain. Neuroimage Clin. 6: 100-108.