What Causes Seizing Of Joints And Purple Rash On Legs?

I am trying to find the name of a rare condition that affected a relative when they were younger. The symptoms included the seizing of leg joints, eventually binding them to a wheel chair for several weeks. A blotchy purple rash appeared on the legs. The condition is something like... xxxx xxxx purplosa or something. Apparently very rare. We fear the condition is coming back, and would like to read up on it until a doctor can be seen. Thanks for any help.