Believe me, when you have a disc protrusion, you're going to have nerve involvement! And at THAT level, it's most assuredly going to be the sciatic nerve, since that's the largest nerve in the body.
You don't have to have stenosis or foraminal narrowing to have nerve involvement, believe me. Sometimes it's even scar tissue. There can be all sorts of things to cause nerve involvement.
So rest assured. You HAVE nerve involvement. LOL God bless. Hugs, Lee