Re: Sis problem
Sure, infections can cause arthritis, but that would be a septic arthritis which is a surgical emergency that can destroy a joint within days. Your sister has chronic inflammation in her joints which has been grumbling on for years now.
The thing with diseases like rhematoid arthritis and gout and even lupus is the fact that, though they often only affect one part of the body significantly (i.e. RA affecting the joints) you have to understand they are systemic diseases and the inflammatory process is going on all over the body. RA and eczema are both autoimmune processes, and a person who has one is at a higher risk of having the other due to the connection in their mechanisms.
There is a certain faction of people who believe that certain low grade chronic yeast infections (i.e. Candida) could be causing symptoms like your sisters. I bring that up only because I think it's fair to show both sides of the coin; however, conventional medicine has shown this to not be true, and it was way back in the 80s. However, I'm not going to knock people who DO believe in the Candida theory, and in fact, there may be some people on the board who know more about it.