It's not as rare as it used to be to have Crohn's disease and Lupus. I have both as well as a slew of other things. I have more "ologists" in my cellphone that any person should ever have. For a year I thought I was going crazy and I would never find any relief. It wasn't until I ended up in the emergency room (while in Cleveland) with severe abdominal pain and ended up having surgery was I diagnosed with Crohn's. My PCP at the time just brushed my pains off as being related to my Lupus. I was in her office more than 10 times in a year complaining of abdominal pain & daily diahrea (sp). My Crohn's was so severe at that point I had to have a portion of my colon removed. While in the hospital the doctors checked, re-checked and triple checked me for Lupus.
The lesson I learned from that experience is never second guess yourself. I knew there was something wrong with me but I kept telling myself she was the doctor. If I had listened to my gut I probably wouldn't have lost part of my colon.
The Cleveland Clinic has a useful article that indicates Crohn's is an autoimmune disorder affecting the digestive tract & mouth whereas lupus affects the heart, joints, kidneys, lungs, skin, nerves and brain. http://www.clevelandclinic.org/health/health-info/docs/1000/1029.asp?index=5865