Piriformis syndrome gets blamed for a lot of leg and buttock pain, so it helps to know exactly what the term says and what it leaves to an exam.
What compresses the nerve
In WebMD's definition, piriformis syndrome is a neuromuscular disorder that is caused when the piriformis muscle compresses the sciatic nerve. So the direct cause in that definition is the muscle pressing on the nerve.
Why the muscle presses on the nerve
Why the muscle ends up compressing the nerve is a separate question, and one for a clinician who examines you. Anyone who lists confident causes without a source is giving you a story and not a record.
Questions to bring to a clinician in Little Falls
If you suspect this condition, tell a clinician where the pain sits and when it gets worse. Ask how they would tell it apart from other causes of sciatica, and what a treatment plan would commit you to over time. For general reading, try the WebMD pain management center, the MedlinePlus sciatica page, the OrthoInfo sciatica page or the American Academy of Pain Medicine.
When the pain needs an exam
Our comparisons stop short of medical advice. A clinician decides what is behind your pain.