There is no particular link between Lyme disease/arthritis and RA. They have totally different causes and generally present very differently. Lyme arthritis usually involves one knee or one ankle, or less commonly two joints. RA usually (but not always) begins in multiple small joints of the hands and feet. Heart block is a definite complication of Lyme disease and very very very rare in RA. The treatment for the two conditions is very very different, so an accurate diagnosis is important. IF in doubt, I would suggest that you take your son to a rheumatologist for further evaluation. Good luck !!