I had similar reactions to Imuran and have always had bad reactions to 5 ASA drugs as well.
Withing 48 hours of starting Imuran I was in the hospital, unable to walk and in isolation until they discovered my liver "failure" was due to the Imuran.
They seriously were going all "House" on me....asking me if I had travelled to foreign countries, running every test they had available. I told them up front that I believed it was a reaction to the Imuran.