It can be both! It can be either or at times; it can be neither if it’s referred pain from your spine or your facet joints. You need to go to a really good orthopedic surgeon and a really good pain management doctor hopefully ones that work together. Also, you should try deep tissue myofascial release therapy that is amazing for piriformis, sciatic and tight SI joints, I’ve suffered with SI joint and piriformis dysfunction for 30 years. I have genetic scoliosis and that caused a problem as I aged. The muscles around your core and spine weaken and they start tugging. You can have nerves that run through your buttocks and you could have tight SI joints , and you can have press on those nerves and cause sciatic pain. There are so many possible combinations of things you can have that you need to see some good doctors who will work together and come up with some viable solutions. Eventually, I had a good deal of surgery done on L3 L4, L5 , and straightening that out helped a lot of the radiating pain that goes down my leg, causing numbness and muscle spasms and a terrible itch on the outside of my left lower leg. There’s something called a nerve conductivity test and your doctors can refer you for that and that’ll isolate where the nerve pain originates , when things get too out of control. I get a shot of Toradol in my buttocks and that resolves the piriformis inflammation and pain for years or months at a time. Nothing substitute for good physical therapy and good stretch exercises and good posture. Also managing one’s weight is really important. I was diagnosed with a piriformis dysfunction early on, and there’s nothing much to be done about it. Nothing magical. Eventually, the diagnosis lead to disc degeneration And stenosis in the facet joints Ulting in a major lower back surgery. It’s really important to go through all the diagnostic functions your doctor and pain management people can put you through. I don’t recommend all the steroids on a regular basis. Just use them purposefully to diagnose , and then figure out what you can do to maintain your body without pain. So use the cortical steroids, the epidurals, the Toradol, and all the things for an immediate treatment but over the long term you have to find other methods to maintain your good health.