Both lupus and rheumatoid arthritis are auto immune diseases.
Lupus and rheumatoid arthritis are pretty similar and share similar symptoms but Lupus is the worse type of arthritis when it comes to types of arthritis.
Rheumatoid arthritis is not fatal but is painful while Lupus Arthritis can sometimes be fatal if not treated properly because the Lupus can attack organs and your own tissue.
As long as Lupus is treated though you can usually live a normal lifespan.
Lupus is caused by inflammation of your joints while arthritis can also be caused by inflammation but also wear and tear on the bodies joints.