Catherine
You need this new diagnosis to make it clear that you were suffering from the problem when you were assessed or you risk it being excluded from any appeal.
I you are going with reliability then make sure you understand the criteria for this, you also need to explain why aids would not be of assistance.
There are links to the SSCS1 that you need to complete are in the PIP MR & Appeal guide, there are also instructions on how to complete the form, you do not need to go into detail as to why your are appealing on the form.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems