Piriformis syndrome occurs when the Sciatic nerve is compressed or pinched by the Piriformis muscle. Indications include sciatica (radiating pain in the buttock, posterior thigh and lower leg) and the physical exam finding of tenderness in the area of the sciatic notch.owever, compression may be present, but not causal, in the setting of sciatica due to piriformis syndrome. The syndrome may be due to anatomical variations in the muscle-nerve relationship, or from overuse or strain.