Mapping of Posture-Dependent Shifts in Paresthesia during Spinal Cord Stimulation (SCS) Cong Yu MD 1, Thomas Yang MD 1, Shaun Kondamuri MD 2, Satish Dasari MD 2, Prakash Rao BS 3, Kerry Bradley MS 3, Lilly Chen MD 3, Nitzan Mekel-Bobrov PhD 3, Jay Schnitzer MD PhD 3 1 Swedish Medical Center, Seattle, WA 2 Midwest Interventional Spine Specialists, Munster, IN 3 Boston Scientific Neuromodulation, Valencia, CA

Disclosures This study was funded by Boston Scientific Neuromodulation. Cong Yu MD serves as a consultant for Boston Scientific Neuromodulation and St. Jude Neuromodulation. Thomas Yang MD serves as a consultant for Boston Scientific Neuromodulation. Prakash Rao, Kerry Bradley, Lilly Chen, Nitzan Mekel- Bobrov, & Jay Schnitzer are employees of Boston Scientific Neuromodulation

Background: Importance of Pain-Paresthesia Concordance “Superposition of stimulation paresthesias upon a patient’s topography of pain was found to be a statistically significant predicator of successful relief of pain.” (North et al., 1991) (North et al., 1991)

Background: Paresthesia Distribution Dorsal CSF layer (dCSF) = distance between epidural contacts and the top of the dorsal columns (DCs). Thickness of dCSF largely influences perception threshold and paresthesia distribution. North, 2006

Background: Posture Causes Changes in dCSF Space “dCSF space not only varies from one level to the spine to another, but also at a given level in a given patient” (Olin et al., 1998) The dCSF space changes with posture due to changes in spinal cord position within the dural sac: Cord is more ventral when sitting, standing, or prone Cord is more dorsal when supine (Olin et al., 1998)

29 patients implanted with Octrode™ leads in cervical and thoracic spine Posture had significant effect on charge/pulse. Significantly higher charge/pulse required when patients in sitting/standing position. Background: Previous Studies on Posture’s Effect on SCS 42 patients trialed with T8-T12 lead placement Measured voltage thresholds with 4- contact perc leads (Pisces™ Quad) Voltage requirements increased when pts moved from supine to sitting/standing positions. How does posture affect paresthesia distribution? Cameron et al., 1998 Olin et al., 1998

Study Design ObjectiveMap shifts in paresthesia distribution associated with changes in posture N13 enrolled subjects Number of Sites2 Subject Characteristics Chronic neuropathic pain of the lower back and/or legs EndpointPatient-reported paresthesia locations recorded at perception threshold in seated and supine positions Study ScheduleSCS permanent implant 2 weeks post-implant 4 weeks post-implant 12 weeks post-implant 26 weeks post-implant 52 weeks post-implant

Methods - + SCS implant procedure Precision Plus™ SCS IPGs 2 Linear™ octapolar percutaneous leads positioned between T8-10 Programming Fixed 8mm ctr-ctr bipole, same lead and contacts used throughout study Pulse width = 500 µs Frequency = 50 Hz Confirmation of lead position by fluoroscopy Data collection with patient in alternative postures seated supine

Results 12 subjects: at least 3 follow-up visits Mean follow-up time: 55±3 weeks post-IPG implant procedure Subjects’ verbal descriptions of paresthesia locations were mapped onto an electronic body map

Results Centroid Analysis: Centroid was calculated by geometric decomposition for each subject’s paresthesia distribution in supine and upright positions, to identify the mean of all points in the shape of the paresthesia across the body. Rostral Shift: Changes in paresthesia distribution between positions were then analyzed as a paresthesia centroid shift with directionality along the three axes. Statistically significant supine-to-upright rostral centroid shift (P<0.05). Supine CaudalRostral

Results Supine CaudalRostral Centroid Analysis: Centroid was calculated by geometric decomposition for each subject’s paresthesia distribution in supine and upright positions, to identify the mean of all points in the shape of the paresthesia across the body. Rostral Shift: Changes in paresthesia distribution between positions were then analyzed as a paresthesia centroid shift with directionality along the three axes. Statistically significant supine-to-upright rostral centroid shift (P<0.05).

Results Dermatomal Preference: Paresthesia locations were remapped to dermatome segmentation. Relative frequency of each dermatome was calculated and compared to expected frequency under random distribution. Statistically significant paresthesia preference in the upright position was found for the anterior dermatomes of the lower extremities L1-L5 (P=0.03) UprightSupine

Discussion: dCSF’s Influence on DC/DR Recruitment Adapted from Holsheimer, 1997 Change in fiber type selectivity Supine Sitting

Conclusions When the patient moves from a supine to upright position: Initial site of paresthesia changes Paresthesia shifts rostrally Paresthesia favors anterior dermatomes in the lower extremities Selective activation of a particular fiber type or a discrete group of fibers may disrupt paresthesia concordance. These observations suggest that changing stimulation amplitude alone does not adequately compensate for shifts in paresthesia distribution due to posture. Common clinical mitigation: creating a therapeutic program dedicated for each position. Each program may have unique amplitude, pulse width, frequency, or anode-cathode programming.