There are several conflicting theories of why Robert Schumann had persistent pain, numbness, and paralysis in his hand. The prevailing lore is that he was impatient and wanted to expedite his virtuosity, thereby creating a device using a cigar box that would enable him to strengthen his fingers.
Others suggest that it was the treatment used for syphilis at the time--either arsenic or mercury poisoning--that caused the neuropathy, and as a result he may have used some sort of contraption to help mitigate the damage.
Another report rejects all these ideas and posits it was 'the musician’s cramp,' a neurological disorder being the ultimate culprit.
We may never come to find out the real answer, but as one scientific article concludes: