Carpal tunnel syndrome (CTS)
CTS is the most common entrapment neuropathy, with a prevalence of 0.2% to 1%. Nine flexor tendons and the median nerve pass through the carpal tunnel, which is narrowest at its mid-portion. CTS occurs when the median nerve is compressed by the flexor retinaculum/transverse carpal ligament at the wrist, producing characteristic nocturnal dysesthesias (70%), but occasionally progressing to sensory loss and weakness of thumb abduction. Pain can radiate into the proximal arm (40%). This condition is bilateral in half of patients and occurs with increased frequency in occupations associated with high levels of repetition and force (meatpackers, shellfish packing, musicians).
Physical examination signs indicative of CTS
CTS, numbness commonly affects the index, middle, and radial side of
the ring finger. The thumb is less often symptomatic. A positive Tinel's sign
occurs when tapping the nerve at the site of entrapment produces pain
and dysesthesias radiating into the sensory distribution of the nerve
distally. In CTS, this test has a pooled sensitivity of 50% and
specificity of 77%. Phalen's Test is positive when passive wrist flexion to 90 degrees for 1 minute produces or worsens paresthesias
in the median nerve distribution. It has a pooled sensitivity of 68%
and specificity of 73% for CTS. The direct median nerve compression test
is positive when pain and paresthesias
occur within 30 seconds of pressure exerted over the carpal tunnel by
the examiner’s thumb. A recently described sign, the volar hot dog
(swelling at the wrist on the ulnar side of the palmaris longus tendon),
has been reported in over 90% of patients with CTS. In addition to
provocative maneuvers, two-point discrimination (sensitivity 25%,
specificity 90%), grip strength, and thenar muscle function and atrophy should be examined. Electrodiagnostic
studies have a sensitivity of 85% and specificity of 95% for CTS.
Ultrasonography and magnetic resonance imaging (MRI) can be useful in
patients with equivocal electrodiagnostic studies.
Diseases associated with CTS (use the mnemonic PRAGMATIC):
Rheumatoid arthritis (any inflammatory arthritis)
Mechanical (overuse, occupational)
Infection (TB, fungal)
Crystals (gout, pseudogout)
Treatment options for CTS:
Nonsurgical therapy consists of avoidance of repetitive wrist motion, cock-up wrist splints at night (and for work), along with antiinflammatory medications. Ergonomic evaluation of the patients’ workplace may be beneficial. In patients with less than 6 months of symptoms, a local corticosteroid injection results in excellent short-term relief in 80% of cases. Indications for surgical therapy (sectioning of the transverse carpal ligament) include failure of conservative therapy, lifestyle limiting symptoms, and muscle weakness or atrophy. Long-term surgical results are favorable in over 75% of patients. Complete recovery of nerve function occurs only if surgery is performed before evidence of denervation on electromyography/nerve conduction velocity.
Other location of median nerve entrapment:
The anterior interosseous nerve syndrome occurs when this nerve, a purely motor branch of the median nerve, is compressed 6 cm distal to the lateral epicondyle. The resulting loss of distal thumb and index finger flexion produces a characteristic flattened pinch sign (inability to form an “O”) with normal sensation. The pronator teres syndrome occurs when the median nerve is compressed by the pronator teres muscle at the forearm, resulting in proximal volar forearm pain that is worsened by grasping and resistive pronation of the forearm. Patients may have numbness of the thumb and the index finger, thumb weakness, and writer’s cramp.