This is another one of those "blanket" diagnoses that has been running amock lately. I find that many parasite infections and high toxin levels can cause restless legs and when they are removed, the symptoms go away.
IBS, fibromyalgia, ADD, ADHD, Chron's, food allergies, food intolerances, depression and others also fit into this catagory of "we have done all the testing that we can do...we don't know exactly what it is...but we think it is _____" (fill in the blank with one of the above).