9.21 Carpal Tunnel Syndrome

agk’s Library of Common Simple Emergencies

Presentation

The patient complains of pain, tingling, or a “pins and needles” sensation in the hand. Onset may have been abrupt or gradual but the problem is most noticeable upon awakening or after extended use of the hand. The sensation may be bilateral, may include pain in the wrist, or forearm and is usually ascribed to the entire hand until specific physical examination localizes it to the median nerve distribution. More established cases may include weakness of the thumb and atrophy of the thenar eminence. Physical examination localizes paresthesia and decreased sensation to the median distribution (which may vary) and motor weakness, if present, to intrinsic muscles with median innervation. Innervation varies widely, but the muscles most reliably innervated by the median nerve are the abductors and opponens of the thumb.

What to do:

• Perform and document a complete examination, sketching the area of decreased sensation and grading (on a scale of 1-5) the strength of the hand.
• Hold the wrist flexed at 90 degrees for 60 seconds, to see if this reproduces symptoms. This is known as Phalen’s test, and is more sensitive than the reverse (hyperextending the wrist) and more specific than tapping over the volar carpal ligament to elicit paresthesia (Tinel’s sign).
• Explain the nerve-compression etiology to the patient, and arrange for additional evaluation and followup. Borderline diagnoses may be established with electromyography (EMG), but cases with pronounced pain or weakness may require early surgical decompression. Anti-inflammatory medication, elevation of the affected hand, ice, immobilization with a volar splint, and rest may all help to reduce symptoms.

What not to do:

• Do not rule out thumb weakness just because the thumb can touch the little finger. Thumb flexors may be innervated by the ulnar nerve. Test abduction and opposition: can the thumb rise from the plane of the palm and can the thumb pad meet the little finger pad?
• Do not diagnose carpal tunnel syndrome solely on the basis of a positive Tinel’s sign. Paresthesia can be produced in the d1stribution of any nerve if one taps hard enough.

Discussion

There is little space to spare where the median nerve and digit flexors pass beneath the volar carpal ligament, and a very little swelling may produce this specific neuropathy. Trauma, arthritis pregnancy, and weight gain are among the many factors which can precipitate this syndrome. Less commonly, the median nerve can be entrapped more proximally, where it enters the medial antecubital fossa through the pronator teres. Symptoms of this cubital tunnel syndrome may be reproduced with elbow extension and forearm pronation.

Illustration

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