idiopathic

adj

1. (not-comparable)Of, relating to, or designating a disease or condition having no known cause.

   “So when I was diagnosed with a fairly difficult-to-treat disease called idiopathic angioedema and chronic urticaria (a fancy way of saying we don’t know why you swell and hey, enjoy the 24/7 hives) six months ago, I wasn't quite sure how to cope.”

   “Juvenile rheumatoid arthritis (JRA), often referred to by doctors today as juvenile idiopathic arthritis (JIA), is a type of arthritis that causes joint inflammation and stiffness for more than six weeks in a child aged 16 or younger. It affects approximately 50,000 children in the United States. Inflammation causes redness, swelling, warmth, and soreness in the joints, although many children with JRA do not complain of joint pain.”