I was so sick and arthritic I could barely move. I had a giant lymphatic swelling thing the size of a small melon on my neck too, I think the diagnosis had to do with the blood work and the lymph nodes, also had a fever over 105 for a week. All my symptoms responded well to gamoglobulin treatment. I also had cardiac contractions, as well as the typical cool-aid-red palms.
I had it again when I was five, but from what I know it is a childhood disease and there have been no cases in anyone over the age of 14.
I do know that without treatment it can cause long-term cardiac complications, but in my case I really had no problems afterwords, aside from a severe childhood fear of needles.