SMP/ Sympathetically Maintained Pain One of the factors common to RSD and Causalgia is that almost all patients will respond to sympathetic blockade (blockage of the sympathetic nerves supplying the area with local anesthetics), which will take away their pain for a variable length of time. However, many patients do not present with the full-blown syndrome that includes all the signs listed above, but do respond to a sympathetic blockade. For example, a patient may come to a doctor with pain only. There may not be Allodynia, there may not be swelling, there may not be muscle spasms or any of the other factors relevant to the diagnosis of RSD. However, a sympathetic blockade takes away their pain. In fact, patients can present with any of the symptoms of RSD on their own. They can present with just swelling, just Allodynia, just burning pain, muscle spasm, etc., and if these people respond to sympathetic blocks, they are then defined as having sympathetically maintained pain or sympathetically maintained pain syndrome sympathetically maintained pain.