Somebody posted a neurology question last week. I have an answer→[More:]
As I said in that thread, which I'm too lazy to find, I asked my dad, who is a neurologist. Here's his reply:

"Without knowing the details, this sounds like the individual has a low back cyst near or compressing a lumbral sacral nerve. The implied treatment is a surgical elimination of the cyst. That surgery would envolve a removal of the dosal(top bone covering) of the spine in order to get at the cyst.

I hope that helps. However, if there is more information let me know."