What Causes Painful And Itching Knots On Hands And Feet?

My mother has been getting knots on her hands, feet, face, and back. They come and go. They look like cysts underneath her skin. Where ever a knot comes up, there will be redness. She states it burns and itchs. She also states they are very painful. She has been to a rheumatology doctor and he said she does not have rheumatoid arthritis. Any hellp would be greatly appreciated.