Any tips for external review for denied prescription?

I've been taking a medication for 20 years, and all of a sudden, my insurance has decided not to cover it. I can't take the recommended alternative because drugs in that class cause a huge flare in my condition. My doctor did a prior authorization – denied. My doctor sent a letter in to appeal – denied. I'm not aware that my doctor was ever given the opportunity to request a peer-to-peer discussion with insurance. Now I've received a letter from some external company that my case has been sent to them for an "independent" review. The letter asked if I wanted to provide additional information. If I understand correctly, this will be the final determination. Does anyone have any tips on how to deal with this? Should I give details of why I can't take the other medication? Is it better to say less, and just let the doctor's letter speak for itself? I need this medicine, and want to up my chances as much as possible, but I feel like the whole process, especially since I had no say in the "independent" company that was hired, is stacked against me. Thanks for any insight.

submitted by /u/Coconuts4488