A 63-year-old man reported numbness in his left first, second and third digits for 2 years. Initially, he found that ‘shaking out’ his left hand helped, but this benefit did not last. He underwent decompression of left-sided carpal tunnel syndrome 2 years earlier and his symptoms worsened after surgery, with more sensory loss and pain. He worked as a carpenter, and had injured his left thumb with nails on multiple occasions without feeling pain. On examination, he had an enlarged left thumb (figure 1), though he appeared unaware of this; his other digits were normal in size. The median nerve was palpable at the wrist, but Tinel's test was negative. There was a mild weakness of abductor pollicis brevis and opponens brevis, with reduced sensation over the fingertips …