Sorry to hear it, but it does raise an important issue.Most of us are aware of the need to avoid strain and injury while playing the piano, but how many of us engage in other activities just as likely to cause this, or aggravate it, without such due regard.
Have you considered an alternate pointing device, such as a trackball?
Wouldn't that be even worse? At least a mouse keeps you mobile to some extent. A trackball locks you in one spot.
There are people that need to do extensive computer work as part of their job, and find a trackball more favorable for long hours of use. All depends on the person. I've seen prototypes of keyboards designed for those with repetitive stress injury. The researchers were suggesting that less movement, not more movement, is the key.
I'd have to say that I'm a little surprised. Having the wrist resting in an a constant spot for long periods strikes me as the worst.