Imagine you’re a world-famous pianist like Leon Fleisher and you’re about to play the first-movement cadenza from Beethoven’s Fourth Concerto, a passage you’ve played hundreds of times. Suddenly and inexplicably, your fingers aren’t responding properly to the messages sent by the brain and the endless hours spent building muscle memory. That could signal the onset of a career-ending disease called focal dystonia.
Source: https://www.sfcv.org/articles/feature/tackling-bane-musicians-existence-focal-dystonia