Isolated sensory impairment of the thumb due to an intraneural ganglion cyst in the median nerve.

We describe an unusual case of digital neuropathy of the thumb due to compression of the median nerve in the distal forearm by an extruded ganglion cyst originating from the radio-scaphoid joint of the wrist. Electrophysiologically, both conduction slowing and block of median motor and sensory axons were present across the cyst. These changes improved after surgery.