What is CRPS, the 'most painful condition' known to mankind?

A 10-year-old old Australian girl has developed incurable Complex Regional Pain Syndrome (CRPS), often called the 'most painful condition' known to mankind. According to Stanford Medicine, CRPS usually affects limbs after injury or surgery and its symptoms are severe pain, swelling, loss of range of motion, temperature changes, and changes in skin. CRPS causes greater pain than a typical injury.