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Difficulty: MediumPhysical Examination Findings

An occupational health clinic evaluates a 38-year-old right-handed carpenter who reports chronic right forearm pain and hand numbness. The symptoms began approximately three months ago. He describes an aching discomfort in the proximal, anterior aspect of his forearm that worsens after extensive use of screwdrivers and heavy hand tools. He also notes tingling in his thumb, index finger, and middle finger. Unlike a colleague who recently underwent surgery for similar hand symptoms, the patient specifically denies being awakened from sleep by the pain. On physical examination, provocative testing with maximum passive wrist flexion (Phalen test) and tapping over the volar carpal ligament (Tinel sign) fail to reproduce the symptoms. However, resisted pronation of the forearm exacerbates the aching pain. Based on the most likely diagnosis, which of the following physical examination findings would distinguish this patient's condition from median nerve entrapment at the transverse carpal ligament?

  1. Decreased light touch sensation over the thenar eminenceAnswer
  2. B
    Decreased light touch sensation over the palmar aspect of the distal index finger
  3. C
    Atrophy of the adductor pollicis muscle
  4. D
    Decreased pinprick sensation over the dorsal web space of the hand
  5. E
    Diminished brachioradialis deep tendon reflex

Answer

Decreased light touch sensation over the thenar eminence
The correct physical examination finding is decreased light touch sensation over the thenar eminence. The patient's clinical presentation—proximal forearm pain exacerbated by resisted pronation, paresthesias in the thumb and index/middle fingers, absence of nocturnal pain, and negative Phalen and Tinel tests at the wrist—is classic for Pronator Teres syndrome. This condition involves entrapment of the median nerve between the two heads of the pronator teres muscle in the proximal forearm. A critical anatomical distinction between Pronator Teres syndrome and Carpal Tunnel Syndrome (CTS) is the involvement of the palmar cutaneous branch of the median nerve. This branch arises approximately 5 cm proximal to the transverse carpal ligament (flexor retinaculum) and travels superficial to the ligament to provide sensory innervation to the skin over the thenar eminence. Consequently, in CTS, the median nerve is compressed deep to the transverse carpal ligament, sparing the palmar cutaneous branch and preserving thenar sensation. In Pronator Teres syndrome, the median nerve is compressed proximally, affecting both the palmar cutaneous branch and the distal digital nerves. Therefore, decreased sensation over the thenar eminence distinguishes Pronator Teres syndrome from CTS.

Step-by-Step Solution

1
Analyze the clinical presentation.
The patient has proximal anterior forearm pain, paresthesias in the median nerve distribution (thumb, index, middle fingers), symptom exacerbation with resisted forearm pronation, absent nocturnal symptoms, and negative wrist provocative tests.
To formulate a differential diagnosis for median nerve distribution symptoms.
2
Differentiate between locations of median nerve entrapment.
The presentation strongly suggests Pronator Teres syndrome (compression between the heads of the pronator teres muscle) rather than Carpal Tunnel Syndrome (compression at the wrist).
Pronator Teres syndrome is characterized by proximal forearm pain exacerbated by pronation and a lack of classic Carpal Tunnel Syndrome signs like nocturnal awakening or positive Phalen/Tinel tests at the wrist.
3
Identify the key anatomical differentiator on physical examination.
The palmar cutaneous branch of the median nerve provides sensation to the thenar eminence. It branches off proximal to the transverse carpal ligament and travels superficially.
Because it travels superficial to the transverse carpal ligament, it is spared in Carpal Tunnel Syndrome. However, it is affected by proximal compressions such as Pronator Teres syndrome, resulting in thenar sensory loss.

Key Concept

The palmar cutaneous branch of the median nerve arises proximal to the transverse carpal ligament, supplying sensation to the thenar eminence; therefore, thenar sensory loss occurs in proximal median nerve entrapments (e.g., Pronator Teres syndrome) but is spared in Carpal Tunnel Syndrome.
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Physical Examination Findings

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