Pathophysiology of Post Amputation Pain

Your participation in this study will last for 5 weeks and you will be asked to come to a total of 3 visits. The first visit will be during the first week of the study, the second visit during the second week of the study and the third (final) visit will be during the fifth (and final) week of the study. For your first visit you will have a physical examination with some sensory stimulation tests (such as vibration and pinprick tests), some questionnaires about your health and pain history, hot and cold sensory tests, and we will take thermal pictures of your body before and after receiving a quick electrical stimulus. You will also be trained on how to use the finger-span device to rate your pain during the second visit, and how to use an electronic pain diary to record your pain scores three times a day during the five weeks of the study. The second visit will begin with questionnaires from the first visit and thermal images with a quick electrical stimulus. You will then be brought to an fMRI scanner room at Northwestern University. For an hour and fifteen minutes we will take pictures of your brain and these pictures will help us understand the changes in your brain relating to pain. You will then be put into one of four treatment groups randomly. The study treatment that you will get will be decided randomly or by chance, like flipping a coin. Injections in this study will use the local anesthetic bupivacaine (a long lasting drug like the numbing agent novocaine used by dentists). This drug causes numbness, blocks pain and other nerve function near the injection site for 6-8 hours. Group 1 will get a sympathetic nerve block of bupivacaine, which changes how your nerves transmit pain, in either the neck or lower back (depending on where the amputation is located), Group 2 will get a placebo injection (no active medicine) in either the neck or lower back (depending on where the amputation is located), Group 3 will get a neuroma injection of bupivacaine (a neuroma is a group of nerves at the end of your residual limb), and Group 4 will get a placebo injection (no active medicine) at the neuroma. Some people get the bupivacaine injection and some people get the placebo injection so that we can compare the groups and see if the bupivacaine brings more, less or the same pain relief as a placebo injection. We scan your brain before the injection so that we can see how your brain responds to pain. We also scan your brain after the injection so that we can see if your brain responds differently to pain after the injection has been done. You will know the location of your injection before you receive the treatment (neck, lower back or neuroma on your affected limb), but you will not know if you are getting a pain medication injection or placebo injection. Only the study doctors will know this information, and it can be told to you in case of an emergency. After the injection, you will have a second hour of brain scanning. After the scanning, you will be asked to complete some questionnaires, sensory tests, hot and cold temperature testing and we will take thermal pictures of your body before and after a quick electrical stimulus. Your third visit will be four weeks after your second visit. For your third visit you will have the same questionnaires as during the first and second visits, sensory tests, hot and cold temperature testing and we will take thermal pictures of your body before and after a quick electrical stimulus.