I definitely get pain from the mouse rather than typing.

Professional Quake players have names for the different styles of holding a mouse. I believe mine is called The Claw, where my palm is a few inches above the matt and I guide the mouse using finger tips on each side, like a bear scraping across the desk.

I notice that when I have pain I have lapsed and my palm is flat on the desk causing a v-shape between my hand and forearm and tension on the back of my wrist.