What can cause swollen fingers and toes?

Consider this: You may have osteoarthritis although early. Blood tests do now show anything. You may want to try to eliminate all dairy, red meat and sugar from your diet for 1 week and see if this improves. I have seen many cases of osteoarthritis mistaken for chronic inflammation due to dietary causes. If it persists, you should see your pcp.

Heat: Is one thing, rheumatoid arthritis is another, some other arthropathies as well, psoriatic arthritis is another. An arthritic work up is warranted assuming it is not heat related.