A 40-year-old postal worker presents to her medical provider…

A 40-year-old postal worker presents to her medical provider with difficulty sorting mail. She feels her hand movements are becoming clumsy and toward the end of her shifts her hands feel tired. On examination, she is asked to press the backs of her hands together as shown in the image below. After 30 seconds she says that she feels her right hand is becoming numb. Which of the following is the most likely diagnosis?