Sciatica, Caused by Disc Herniation Caused by Piriformis Syndrome, Compressed S1 nerve (routine disc herniation) Compressed L4 nerve (far lateral disc herniation)Sciatica is a painful symptom of another condition. A herniated disc or swollen piriformis muscle (piriformis syndrome) can compress the sciatic nerve causing referred pain which can reach from the lower back all the way down to the foot. MendMeShop TM ©2011