What are the initial studies performed in the workup of carpal tunnel syndrome (CTS)?

Updated: Mar 30, 2020
  • Author: Nigel L Ashworth, MBChB, MSc, FRCPC; Chief Editor: Milton J Klein, DO, MBA  more...
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Answer

Electrophysiologic studies, [3, 4, 5] including electromyography (EMG) and nerve conductions studies (NCS), are the first-line investigations in suggested carpal tunnel syndrome (CTS). [6] Abnormalities on electrophysiologic testing, in association with specific symptoms and signs, are considered the criterion standard for CTS diagnosis. In addition, other neurologic diagnoses can be excluded with these test results. NCS in a patient with CTS are seen in the images below.

Sensory nerve conduction studies from the left han Sensory nerve conduction studies from the left hand of a patient with a several-year history of numbness and weakness (responses from the median nerve in the right hand were completely absent). Note marked slowing of the conduction velocity (CV) to 29.8 and 25.5 m/s for digits 3 and 1, respectively (normal >50 m/s). The amplitude for both also is reduced markedly (normal >10). These findings are consistent with carpal tunnel syndrome.
Motor nerve conduction studies from the left hand Motor nerve conduction studies from the left hand of a patient with a several-year history of numbness and weakness (responses from the median nerve in the right hand were completely absent). Note that the conduction velocity (CV) across the carpal tunnel segment slows severely to 18.3 m/s (normal >50 m/s) and that the distal motor latency is prolonged at 6.3 ms (normal < 4.2 ms). Amplitudes are low for the wrist and elbow stimulus sites at 4.7 mV (normal >5 mV), but amplitudes are 31% higher distal to the carpal tunnel (at the palm). This discrepancy may represent conduction block (neurapraxia) at the level of the carpal tunnel or coactivation of the ulnar branch to adductor pollicis. Needle electromyography is required to determine whether axonal loss is present.

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