Repetitive stress injury is notoriously hard to diagnose, a fact that has turned it into one of those is-it-or-isn't-it-type conditions whose existence is doubted.
But that may be about to change. I'm working today on a story for Wired News about a study that says doctors might be able to find "biomarkers" in people with repetitive motion injures. That could help confirm that patients have the condition or at least warn them to start watching their activities so things don't get worse:
Biomarkers warn of impending injury from repetitive motion [press release]