What qualifies a pain specialist to be able to treat fibromyalgia?

Caring interest. Doctors don't learn everything in medical school. Worse yet, medical knowledge and technology change so fast that most of what each doctor uses everyday must come from keeping up with the latest scientific publications. This is especially true with fibromyalgia, where the first drug was approved by fda just a few years ago. Many doctors are qualified, if they have an interest and keep up learning.