Elsevier

Neurologic Clinics

Volume 30, Issue 2, May 2012, Pages 457-478
Neurologic Clinics

The Electrodiagnostic Approach to Carpal Tunnel Syndrome

https://doi.org/10.1016/j.ncl.2011.12.001Get rights and content

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The gold standard question and the role of electrodiagnostics

The gold standard for the diagnosis of CTS has been debated. CTS is a clinically defined constellation of symptoms caused by a median neuropathy at the wrist (Box 1).6 Clinical examination signs, such as the Tinel and Phalen signs, are not included in the proposed criteria, as they are limited in specificity. A Tinel or Phalen sign has been reported in 20% or more of healthy subjects.7, 8, 9 Similarly, there can be misdiagnoses (false-positives) with the clinical symptoms alone.10

The electrodiagnostic evaluation for CTS

A practice parameter for electrodiagnostic studies in carpal tunnel syndrome was published in 2002 after being endorsed by the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM), the American Academy of Neurology (AAN), and the American Academy of Physical Medicine and Rehabilitation (AAPMR),18, 21 with its full details and annotated bibliography published in a supplement.6 This still serves as an excellent review and the pooled sensitivities and specificities for CTS

Technique

Recording ring electrodes are placed over the second digit (pointer finger) with G1 over the proximal phalanx and G2 over the distal part of middle phalanx.22 The median nerve is stimulated 13 cm proximal to the G1 electrode just above the wrist where it runs between the easily palpated flexor carpi radialis tendon radially and the palmaris longus tendon medially. More proximal stimulation can be performed over the median nerve in the antecubital fossa, medial to the biceps tendon overlying the

Technique

The G1 recording electrode is placed at the midpoint of the abductor pollicis brevis (ABP) muscles on the thenar eminence one-third the distance between the major creases at the metacarpal-carpal and metacarpal-phalangeal joints of the thumb.22 G2 sits just distal to the metacarpal-phalangeal joint on the lateral side of the thumb. The stimulator cathode is placed 7 cm proximal to G1 over the median nerve between the flexor carpi radialis and palmaris longus tendons.

Normal values

Normal values are distal

The role of electromyography—the needle examination

The role of the needle examination in CTS has been debated in the literature.65, 66 On one side, it is argued that if the clinical suspicion was for CTS and the NCS confirmed that diagnosis, the needle EMG adds little except discomfort and cost. The counter argument is that confirming the diagnosis is only one of the roles of electrodiagnostic studies in CTS. It is just as important to exclude mimickers and processes that, if present (cervical radiculopathy or peripheral neuropathy), may cause

Peripheral Neuropathy

Identifying CTS in patients with superimposed peripheral neuropathies can be challenging both clinically and electrophysiologically. It can be difficult to determine if the median NCS distal latency prolongation is disproportionate to the changes seen in other NCS. A comparison latency study would seem most appropriate for this determination, as the peripheral neuropathy would be expected to affect both the median and ulnar nerves similarly. The lumbrical–interossei motor studies have been

Putting it all together—a treatment algorithm

Box 4 presents a suggested algorithm for the electrodiagnostic approach to the patient with suspected CTS. It incorporates the AANEM/AAN/AAPMR practice parameter guidelines and quality recommendations.20, 21

Summary

CTS is a clinically defined syndrome; however, there is value added by an evidence-based electrodiagnostic approach to (1) efficiently confirm the diagnosis (particularly before invasive interventions), (2) to identify neurogenic mimickers or superimposed processes that may influence the response to treatment, and (3) to stratify the degree of neurogenic injury to help the clinician make management decisions in conjunction with the severity of the clinical symptoms.

Take-Home Points:

  1. 1.

    CTS is a clinically defined

Acknowledgments

I acknowledge Dr J. Clarke Stevens, a Mayo Clinic professor of neurology, electrophysiologist, and respected expert in CTS, whose mentorship and knowledge were instrumental in developing my CTS curriculum, which served as the basis for this article.

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    Disclosures: no pertinent disclosures.

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