One doctor thinks the symptoms in my arm and hand are coming from carpal tunnel syndrome. Another says the problem is thoracic outlet syndrome. Who is right?

They both may be right. It is well documented that both conditions can happen at the same time. Both syndromes are caused by doing repeated activities with the hands and arms. And they both cause similar symptoms.

One theory about why these conditions happen together is called the double crush phenomenon. Pressure at one end of the nerve path can set the stage for problems at the other end--a double crush. In this theory, pressure problems in the carpal tunnel in the hand can actually lead to problems at the other end of the nerve, near the thoracic outlet. The opposite is true too. Pressure near the thoracic outlet can end up causing problems of carpal tunnel syndrome at the other end of the nerve.