arhthritis treated with remicade yet undiagnosed

my mother suffers from an arthritic condition but, has not been diagnosed with a specific condition. i do not know much about all the different types of arthritis i am just trying to understand this. anyone else have these problems of not being diagnosed with a specific condition?

and lets not forget the trial and error technique that rheummies use to diagnose, "if this works...then you do have RA!" i got that response from a doc in NYC. but he said it's true. sometimes labs are so inconclusive that the only way to pinpoint a disease is if it responds to the treatment.
what an art