When BC/BS Federal denied our first pex, I wrote a letter of appeal. Basically, my son was totally incapacitated at the time. Having dealt with years of occupational therapy and my sick elderly father, I remembered that somewhere in that black hole of insurance rules that they are required to see that the patient be able to achieve all the normal daily activities of living...Eating, Bathing, Toileting, Walking/Movement, Sleeping, Dressing. These can vary depending on what you look at, but basically these are it. Most often they are used with elderly patients, but I figured why not with my son...he couldn't do any of these. So I took each activity and explained to the insurance company how he couldn't do them or how difficult they were. Basically, I said this is what's wrong, and by using the daily activities of living I left the ball in their court.
We got approval, but it was rather strange how it happened. The same doctor who denied before denied it again. Then a few days later I got a call saying it was approved from one department as well as our doctor's office. About 20 minutes later the bad doctor's secretary called me saying it was denied (i had left an interesting voice mail for him earlier that day I informed them I was just told it had been approved and she had no idea what I was talking about. Good thing I was taking names!! It was funny in 1 hour's time I got 3 calls from 3 different area codes discussing this issue!! Anyway, I think we lucked out with a very sweet nurse, Donna - I'll never forget the name, who took the letter to the right desk and got it improved.
Ugh...I probably haven't helped you! Basically, it was luck, but I do think the letter helped lay it out clearly for the insurance company. And that using the "normal daily activities of living" gave them more responsibility. I know you said your son was doing better, so maybe you could go back and state you don't want to go backwards or something, and that prevention is the normal standard of care for autoimmune diseases.
We didn't find out about the patient advocate until after either. Funny how that stuff isn't made clear.
Well good luck and my best!!