I was just rated 20%. My question is they didn't rate my peripheral neuropathy along with my DMII. So, which form should I use to send them my doctor's notes about the relation between DMII and peripheral neuropathy?
Good news! You don't need a form. Once a veteran has filed a VA Form 21-526 there is no future need to duplicate that.
To make a new claim or to ask for an increase or modification of an existing claim, all you need to do is write a letter.
In the letter explain precisely yet briefly what it is that you want. There are sample letters available of my A to Z Guide at http://jimstrickland912.com
Enclose copies of any evidence you have to support your claim. Send the letter using certified mail, return receipt requested and VA will respond to that.