As Paul says, the brachial plexus nerve bundle is most likely the cause. Everything branches to the chest and arms from there. I believe it is very treatable and managed, although, not so with any clipped nerves from surgery. They can heal but it takes years. I was diagnosed with brachial plexopathy and after trying many medications, I went a different route using a specialized neurological chiropractor. I wouldn't suggest this route if you aren't very active. One thing to watch for is progressive difficulty breathing as the nerves through the chest are key to breathing.