A disc herniation at one level in the thoracic spine will not by itself cause another disc herniation at a different level. That being said, you may have a genetic predisposition for disc herniations.
Over time, many symptomatic thoracic disc herniations will “heal” or become much less symptomatic. Some don’t and need treatment like epidural injections or facet blocks. Rarely, one might need surgical intervention.
It is exceedingly rare to have a thoracic disc herniation cause leg pain. I have seen one case in my career. A thoracic disc herniation will not cause arm symptoms.
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.