Sjogren's Syndrome Support Group
Sjogren's syndrome is an autoimmune disorder in which immune cells attack and destroy the exocrine glands that produce tears and saliva. It also associated with rheumatic disorders such as rheumatoid arthritis, and it is rheumatoid factor positive in 90 percent of cases.
The piriformis is a muscle that lays underneath the gluteal muscles in the buttock. The sciatic nerve can sit just underneath the piriformis, on top of it, or through it. If that muscle is tight, it can impinge the sciatic nerve, causing pain in the lower back and down the leg. I've included links to two pictures that show this. If you can find well educated massage therapist (specializing in deep tissue, sports massage, or medical massage) or a physical therapist, they can show you how to massage (to relax the muscle) and how to stretch it. You can also try heat in an attempt to relax the muscle. You'll want to apply the heat to the buttock, not the lower back, to specifically affect the piriformis muscle.
I hope this helps!
http://www.massagetoday.com/content/images/lowe02__1_1_6984.jpg http://jonaschiropractic.com/wp-content/uploads/2017/02/Sciatica-or-Piriformis.png