The carpal tunnel syndrome should be considered when there is any unexplained pain or sensory disturbance (e.g., intermittent numbness and acroparesthesia of the hand that is worse at night) and weakness of the abductor pollicis brevis, the lateral two lumbricals, the opponens polli-cis, and the flexor pollicis brevis muscles. Carpal tunnel syndrome occurs as a result of compression of the median nerve beneath the carpal tunnel ligament, and affects 1 % of the population.
The following physical tests can be helpful in the diagnosis of carpal tunnel syndrome.
- Median nerve percussion test. The test is positive when tapping the area over the median nerve at the wrist produces paresthesia in the median nerve distribution. Sensitivity 44%, specificity 94%
- Carpal tunnel compression test. The test is considered positive when the patient's sensory symptoms are duplicated after pressure is applied over the carpal tunnel for 30 seconds. Sensitivity 87%, specificity 90%
- Phalen wrist flexion test. This test is positive when full flexion of the wrist for 60 seconds produces the patient's symptoms. Sensitivity 71 %, specificity 80%
- Electrodiagnostic tests. Sensory conduction studies are the most sensitive physiological technique for diagnosing carpal tunnel syndrome. Abnormal sensory testing can be found in 80% of patients with minimal symptoms and in over 80% of severe cases, in which "no recordable sensory potentials" are observed. Normal nerve conduction studies are found in 15-25% of cases of carpal tunnel syndrome
Electromyography is normal in up to 31 % of patients with carpal tunnel syndrome. Abnormal electromyography with increased polyphasic quality, positive waves, fibrillation potentials, and decreased motor unit numbers of maximal thenar muscle contraction, is regarded as severe and as an indication for surgery
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