Piriformis syndrome is what many doctors call an entrapment neuropathy. In simple terms, that means that a muscle deep in the gluteal area (the piriformis) is tight and/or inflamed which decreases the conduction or flow of the largest nerve in the body (the sciatic), which lies nearby. Pain can be in or around the piriformis muscle, or along the distribution of the sciatic nerve, most of the time this is in the back of the thigh, but possibly all the way down into the foot. Someone that has shooting pain along the sciatic nerve  is often diagnosed with sciatica.  Pain can also be referred up into the lower back region.