The Electrodiagnostic Approach to Carpal Tunnel Syndrome
Section snippets
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: 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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Cited by (24)
The Association Between Electrodiagnostic Severity and Treatment Recommendations for Carpal Tunnel Syndrome
2021, Journal of Hand SurgeryCitation Excerpt :Furthermore, wait time between EDS and CTR was inversely correlated with EDS severity, with severe EDS patients having the shortest time between testing and surgery. Previous studies have debated the utility of routinely grading CTS severity by EDS criteria given that nerve conduction study results often are not correlated to severity of symptoms.14,15,17 However, other authors have argued that EDS severity has value for prognosis and for assessment of treatment outcomes.13,28
Comparative study between physical examination, electroneuromyography and ultrasonography in diagnosing carpal tunnel syndrome
2014, Revista Brasileira de OrtopediaColchicine treatment in children with familial Mediterranean fever: Is it a risk factor for neuromyopathy?
2013, Pediatric NeurologyCitation Excerpt :In the present study, NCS identified asymptomatic CTS in only one patient. As in this patient, previous studies have reported that only sensorial conduction abnormality is observed.10 In addition, CTS is known to possibly develop secondarily to systemic amyloidosis.11,12
Giant lipoma of the forearm as a cause of extracarpal compression of the median nerve
2013, Reumatologia ClinicaTiming and appropriate use of electrodiagnostic studies
2013, Hand ClinicsCitation Excerpt :When the results are similar to preoperative studies, the interpretation is less clear because EDS does not return to normal after carpal tunnel release and may have minimal change with adequate decompression.29 These are most helpful when performed by the same electromyographer who performed the original studies because this eliminates the variability between centers and individuals.17 EDS is helpful in defining median neuropathy other than CTS.
An open-label pilot study evaluating the effectiveness of the heated lidocaine/tetracaine patch for the treatment of pain associated with carpal tunnel syndrome
2014, Pain PracticeCitation Excerpt :Diagnosis of CTS is usually made by medical history and physical examination that is suggestive of median nerve entrapment.1,2 Electrodiagnostic testing can identify delayed median nerve conduction and can be used to confirm a diagnosis of CTS.7 However, some patients with clinically confirmed CTS fail to exhibit a nerve conduction abnormality, and some totally asymptomatic patients may demonstrate electrophysiological median neuropathy upon testing.8
Disclosures: no pertinent disclosures.