Is this evidence? Pip appeal

When I first applied for PIP I told them about my symptoms and initially I'd put down that these symptoms were caused by migraines. However I'm in the process of appealing their decision, and have just being diagnosed with Fibromyalgia. It turns out that although I do suffer with migraines a lot of my symptoms have actually been caused by the Fibromyalgia. Would it be a good idea for me to send a doctors letter explaining this new diagnosis? I know the importance of making sure any evidence or new information is related to the initial reason for appealing and I feel that I have suffered with fibromyalgia for a long time but at the time of applying for pip we were not aware that's what was actually causing some of my health problems. The only thing that has changed is the condition, I'm still suffering the same way! Well, things are worse now if anything as I've developed more symptoms but I am aware this isn't relevant to the original appeal.

Apologies if anything doesn't make sense I am totally overwhelmed with fatigue at the moment.

Oops apologies. I have already lodged the appeal and I'm just waiting for the tribunal date.
I did actually get a call from PIP last week, they asked if I had any extra information for them before they sent responded to the tribunal and if I did have any more evidence to add that they may phone me again before the tribunal date to see if we can come to an 'agreement'. So I'm really hoping if I can explain myself properly with this new diagnosis it'll mean they change their mind before it gets to the hearing.

Wishful thinking maybe...