Evidence-Based Physical Exam: Carpal Tunnel Syndrome

Background

Carpal tunnel syndrome (CTS) refers to the symptoms and signs caused by compression of the median nerve as it travels through the carpal tunnel. Patients commonly experience pain and paresthesia, and less commonly weakness, in the distribution of the median nerve. CTS is the most frequent compressive focal mononeuropathy seen in clinical practice, affecting 1-5% of the general adult population.

Symptoms may be noted initially at night with pain or paresthesias waking patients from sleep, and during the day are often provoked by activities that involve sustained flexion or extension of the wrist, such as driving, reading, typing, and holding a phone. Symptoms sometimes progress from intermittent to persistent sensory complaints and from paresthesias to sensory loss in the hand. 

CTS typically spares the thenar eminence and palm because the palmar cutaneous branch of the median nerve arises proximal to the wrist and passes over, rather than through, the carpal tunnel.

Motor symptoms, including weakness, typically develop late and in patients with a more severe course.

Evidence-Based Physical Exam

Three findings modestly increase the probability of CTS:

• Diminished pain sensation in the distribution of the median nerve (LR = 3.1)
• A “classic” or “probable” hand diagram (LR = 2.4)
  • Self-administered diagram of the hand that depicts the patient’s symptoms: the “classic” pattern describes symptoms affecting ≥2 of digits 1, 2, or 3 but sparing the palm and dorsum of the hand; the “probable” pattern is similar to the classic pattern, although palm symptoms are allowed; the “unlikely” pattern depicts symptoms not involving digits 1, 2, or 3. Palm symptoms are not part of the “classic” pattern, because the palmar cutaneous branch of the median nerve does not travel through the carpal tunnel.

• Weak thumb abduction strength (LR = 1.8)

Three other findings show promise in increasing the probability of CTS, but each is based on limited data and more studies are needed: 

• Flick sign
  • When asking the patient, “What do you actually do with your hand(s) when the symptoms are at their worst?” the patient demonstrates a flicking movement of the wrist and hand, similar to that used in shaking down a thermometer
• Closed fist sign
  • Paresthesias in the distribution of the median nerve when the patient actively flexes the fingers into a closed fist for 1 minute
• Square wrist ratio
  • The anteroposterior dimension of the wrist divided by the mediolateral dimension equals a ratio of greater than 0.70, when measured with calipers at the distal wrist crease

Two findings decrease the probability of CTS: 

• An “unlikely” hand diagram (LR = 0.2; see figure above)
• Normal thumb abduction strength (LR = 0.5)

Traditional tests such as the Tinel sign and Phalen sign fail to distinguish CTS from other common disorders causing hand dysesthesias (e.g., polyneuropathy, ulnar neuropathy, or radiculopathy, using electrodiagnosis as the diagnostic standard.)

• Tinel’s test = Firm percussion over the course of the median nerve just proximal to or on top of the carpal tunnel. A positive test is defined as pain and/or paresthesia of the median-innervated fingers that occurs with percussion over the median nerve.
  • Sobering fact: Up to 45% of asymptomatic, healthy patients may have a positive Tinel sign
• Phalen’s test = Patient brings the dorsal surfaces of the hands against each other to provide hyperflexion of the wrist while the elbows remain flexed; the flexed position is held for 1 minute. A positive test is defined as pain and/or paresthesia in the median-innervated fingers.

Further Reading!

• Steven McGee’s Evidence-Based Physical Diagnosis
• JAMA’s The Rational Clinical Examination

Blog post based on Med-Peds Forum talk by Julia Solomon, PGY3, and Cameron Ulmer, PGY2