Rheumatoid Arthritis Support Group
Rheumatoid arthritis is a chronic, inflammatory, multisystem, autoimmune disorder. It is a disabling and painful condition which can lead to substantial loss of mobility due to pain and joint destruction. The disease is also systemic in that it often also affects many extra-articular tissues throughout the body including the skin, blood vessels, heart, lungs, and...

I would guess maybe a blister or nodule. Ive read early nodules can be soft, but turn hard. They tend to be on high friction areas. The only thing, though, is I read they don't hurt. So I'd assume possibly a blister. Either way photos can help, so if it goes away you can show your rheumatologist and ask them next time you see them. Also I read this
http://my.clevelandclinic.org/orthopaedics-rheumatology/diseases-conditions/benign-soft-tissue-tumors.aspx
Could be fat cell lipoma or something similar. Benign soft tissue tumor. It it doesn't clear or gets worse, I'd go to the gp and tell them "im concerned I have a soft tissue tumor".
That way they'll check you for that specifically...and not "miss diagnose". I find it I research and ask if what I have is x y or z, then if the doctor is, um, not well educated on more rare conditions, bringing up my specific concerns can help the doctor consider all medical options and not blow me off.
Hi Cindyleb. I deal with Baker's Cysts behind my knees. I am new to them but wonder if they could occur on other parts of the body -- not just the knees. Maybe it's worth a google to check out Baker's Cysts to see if this sounds like your lump and of it could be one on your ankle. Maybe not. Just trying to think of RA things that might lead you on the right direction.
In any case I am sorry you are dealing with this. Hugs to you.