Stringsinger, if I had reason to really suspect that nightshades were causing my arthritis, I might take the (to me) draconian measure of never eating any potatoes, tomatoes, okra, peppers, eggplant, tomatilloes, etc. But I've been diagnosed with osteoarthritis, and the location of my arthritic joints clearly suggests wear-and-tear from heavy use as the culprit. (E.g., the worst nodes are on my my left hand (as is most of the stiffness) and in the location of an old injury to my big toe. I don't seem to have arthritis in my wrists or ankles, or most of the other joints of my body.) Plus my screenings for rheumatoid arthritis keep coming up negative.
It may seem a minor thing to eschew nightshades, but though I rarely eat potatoes or eggplant or peppers, giving up tomatoes and tomato products would mean giving up on a number of health benefits that they provide. Plus, so many salads, soups and other dishes contain tomatoes or tomato sauce, that it's not that easy (or desirable) to cut tomatoes out entirely. I'd do it if I were convinced they were a likely source of osteoarthritis. But I just haven't come across any sound evidence to convince me that eating tomatoes contributes to the stiffness and the loss of cartilage in the joints of my chording hand.