Ask you doctor to check for thoracic outlet syndrome. You might instead have a stretch radiculopathy (called a stinger or burner) if you had a fall onto that outstretched arm. There are also entrapment syndromes (carpel tunnel and cubital tunnel syndrome) that can occur. Ask your physician to check for those also.
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.