Guyon's canal syndrome is much less common than carpal tunnel syndrome (CTS), yet both conditions can occur at the same time. The numbness caused by these two syndromes affects the hand in different locations. When the median nerve is compressed in CTS, pain and numbness spread into the thumb, index finger, middle finger, and half of the ring finger. Compression of the ulnar nerve in Guyon's canal syndrome usually causes numbness in the pinky and half of the ring finger.