Also suggesting an anti-inflammatory diet. Cut out sugar, grains, dairy. Nightshades as noted above are commonly mentioned in conjunction with arthritis. Sweet potatoes are not in the nightshade family. Black pepper is not in the nightshade family to my knowledge; paprika comes from a particular variety of sweet pepper and that's why it is included.
Turmeric, in combination with black pepper in particular, is noted to be anti-inflammatory. Turmeric can be added to many dishes without causing a noticable color or flavor change, if the quantity is fairly low - no need to limit it just to curries.
This website has many interesting articles and short (3 minute) videos on a nutrition topics. The author, an M.D., discusses findings in recent peer-reviewed journal articles. Here is a link to the videos about arthritis and diet. Note, however, he has a strong vegan slant.
http://nutritionfacts.org/topics/arthritis/