I never believed vegetables in the nightshade category could precipitate arthritis. I do now!
I love fried green tomato sandwiches. So last year I grew at least 10 types of tomato plants. I ate fried green tomatoes almost daily. My pains increased. "No this couldn't be" I thought. But yes, unfortunately it was true. I tried frying the tomatoes without cornmeal as well as with and without flour. None of this made any difference. Now I occasionally eat a ripe tomato but rarely fried green tomatoes. As much as I love fried green tomatoes, I love being pain-free more.
Nightshades contain alkaloids or Solanaceae. If you are sensitive to these compounds, nightshades could flare up your arthritis.
Here's a list of some other Night Shades