Blocks are often used as a diagnostic tool, as well. Relief, even for a short period, confirms RSD is the correct diagnosis.

The skill of the doc perfeorming the block can make a big difference as well.
I had some done by the local pain mill doc, and others by a former spine surgeon, turned pain doc. The second were harder on me (I was awake and my reactions helped him pinpoint the area) but vastly superior.

The pain mill doc's were more hit or miss, where as the spine doc's blocks all lasted 2+weeks.

Just make sure you're getting the best RSD care available in your area.