It does sound an awful lot like a lupus rash to me. According to what I've read, arthritis patients that respond well to plaquenil lean toward the lupus side of things (or rhupus, if you will). You will definitely want to mention this to your doctor, and try to take a picture of it if you can. When I went off plaquenil, I did not have any problems at all. I also understand that enbrel can make things worse for lupus patients, but I know several lupies that take enbrel for arthritis, so I don't know if there's a lot of research to support that statement.
Current dx: Rheumatoid Arthritis
Suspected dx: UCTD/Early Lupus
Current Meds: Enbrel, Plaquenil, Methotrexate, nexium, tramadol, nasonex,Tylenol PM
Past Meds: Relafen, Vioxx, Mobic, Voltaren, Sulfasalazine, Entocort, Prednisone, Humira, Reglan, zyrtec, zegerid, aciphex