A 27-year-old woman visits her obstetrician for a routine prenatal exam. She is 29 weeks pregnant with her first child. Her only new complaint is two weeks of numbness in her hands that has been causing her to drop objects she is holding throughout the day. She reports that the numbness is worse in the morning and characterizes the sensation as "pins and needles." On physical examination, tapping just superficial to the flexor retinaculum reproduces the sensation. She exhibits a positive response to the Phalen maneuver. There is significant loss of sensation to light touch over the ventrolateral digits (thumb, index, and middle fingers).
Which of the following nerves is compromised in this patient?
A) Axillary nerve
B) Median nerve
C) Musculocutaneous nerve
D) Radial nerve
E) Ulnar nerve
B) Median nerve
This patient is experiencing symptoms of carpal tunnel syndrome, which include pain, numbness, and tingling in the thumb, index, and middle fingers. Patients may also exhibit decreased grip strength. Obesity, pregnancy, repetitive use of the wrist, and rheumatoid arthritis are risk factors for the development of carpal tunnel syndrome. The nerve responsible for causing these symptoms is the median nerve. On physical examination, the physician can perform two diagnostic maneuvers. The first is eliciting the Tinel sign, which is performed by tapping just above the median nerve as it passes through the carpal tunnel at the wrist. A positive sign elicits a tingling sensation in the distribution of the median nerve over the hand. The Phalen maneuver requires the patient to allow the wrists to fall freely into maximum flexion and maintain the position for 60 seconds. If the patient has carpal tunnel syndrome, this will also elicit a tingling sensation in the distribution of the median nerve.
Key Learning Point
Carpal tunnel syndrome is a complex of symptoms and signs due to compression of the median nerve as it travels through the carpal tunnel. Pain and paresthesias typically occur in the median-innervated fingers. More severe cases may result in weakness or clumsiness when using the hands.
