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“Poly-arthritis is the type of JIA that tends to cause painful swelling in fingers, toes, wrists, ankles, hips, knees, and the neck and jaw. This type of JIA can affect 5 or more joints in the first 6 months, often the same joints on each side of the body. It may come on suddenly or can steadily involve more joints over a period of months”.

You may find below link useful to get more information on same.
http://my.clevelandclinic.org/childrens-hospital/health-info/diseases-conditions/hic-Juvenile-Idiopathic-Arthritis

Anna.