Effect of Spinal Cord Stimulation on Pain Thresholds and Sensory Perception in Chronic Pain Patients.

Sixty subjects who already have an implanted SCS device for pain management at the MGH Center for Pain Medicine and other Partners affiliated pain centers will be enrolled. Inclusion Criteria: 1. Subject is 18 years or older. 2. Subject has an SCS device implanted for at least one month for pain control. This requirement is set to ensure that the subject becomes familiarized with the therapy and has recovered from the surgical implantation of the SCS device. Exclusion Criteria: 1. Subject has neurological disease or a condition causing sensory deficit to the painful area. 2. Subject had recent therapy that may influence QST results, e.g., neuroablative procedure within two-months. 3. Subjects who are unable to travel to the study center. It will be a one time outpatient visit study, which will include the following: 1. Brief pain history and Neurological examination * Medical History (including medication use); * Pain location, intensity, character and if known, etiology, duration; * Maps of pain locations and paresthesia locations; * Sensory neurological examination (e.g., alcohol swab, cotton swab, pinprick and vibration); * A check on routine vital signs (blood pressure, pulse, pulse oximetry). 2. QST will include the following: * Warm sensation, heat pain threshold, heat pain tolerance and wind-up. A cut-off of 53°C for heat will be preset to avoid tissue damage. * QST will be done on two areas; painful area and non-painful area without paresthesia with the SCS turned off. * Subject will then turn on SCS and a repeat QST will be performed on the painful and non-painful areas. * QST tests will be performed in a quiet room at temperature 25º 2° C. The time and duration of the QST tests will be recorded. QST will be performed at least 4 hours and no later than 6 hours after the last dose of long acting opioid and after last SCS on time. In this way the investigators will try to avoid recording possible end dose withdrawal and provide sufficient time for the subject to return to baseline for their SCS therapy.