COMMENTARY

Electrodiagnostic Testing in the Diagnosis of Carpal Tunnel Syndrome

April 28, 2009

Introduction

Median nerve entrapment, also known as carpal tunnel syndrome (CTS), is a commonly seen entity by primary care physicians and orthopaedic specialists alike. It is the most common nerve entrapment in the body.[1] This condition is often diagnosed clinically based on nonstandardized features from the patient history and physical examination. The workup for CTS may also include electrodiagnostic testing, which can further define the presence and severity of peripheral nerve and/or muscle pathology.

The Value Added by Electrodiagnostic Testing in the Diagnosis of Carpal Tunnel Syndrome

Graham B
J Bone Joint Surg Am. 2008;90:2587-2593

Summary

Dr. Graham conducted a prospective, randomized, blinded study that compared the probability of the presence of CTS after electrodiagnostic testing with the pretest probability of diagnosis using the CTS-6 assessment tool, a validated clinical diagnostic aid.

A hand therapist established the pretest probability of CTS in 143 patients using the CTS-6 assessment tool. Subsequently, a nerve conduction study test was performed on all patients, and a neurologist blinded to the CTS-6 assessment results evaluated the data. The median sensory nerve velocity was measured over an 8-cm segment from the proximal carpal tunnel to the middle finger. Specifics of the electrodiagnostic testing were otherwise not specified. The pretest probability of CTS ranged from 0.10 to 0.99, with more than 73% of patients having a pretest probability above 0.80. The average change in probability after electrodiagnostic testing ranged from -0.06 to -0.02, which lowered the probability in most cases.

Viewpoint

This study by Dr. Graham demonstrates the clinical potential of adding the CTS-6 assessment tool to a comprehensive history and physical examination in diagnosing CTS. In unambiguous cases of CTS, electrodiagnostic testing would not be warranted if its sole purpose is to confirm the diagnosis of CTS.

Electrodiagnostic testing is and should be considered an extension of the physical examination. As such, its value in this situation is not only to confirm a physician's suspicion of CTS, but also to quantify and stratify the severity of the condition. Often, a patient's degree of symptoms does not correspond with electrodiagnostic study abnormalities.[1] Patients who have mild delays in median nerve velocities, for example, could be treated more conservatively than those who have significant abnormalities suggestive of moderate or severe disease. Furthermore, electrodiagnostic testing has been used as an objective preoperative and postoperative measure of nerve function.[2,3]

Electrodiagnostic studies are also valuable in patients who may not have a simple clinical picture. In addition to ruling in a diagnosis, it can rule out other causes, such as a pronator syndrome, a cervical radiculopathy, or a generalized peripheral neuropathy.

One notable limitation to this study was the lack of delineation of the electrodiagnostic study protocol. As the author mentions, there are several nerve conduction study protocols for CTS. The study's main focus was median sensory nerve latency. Current American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM) practice guidelines recommend an initial screen using a 13- or 14-cm distance for the median sensory nerve study. Rather than relying on an absolute nerve latency measurement in isolation, the subsequent use of side-by-side comparison nerve studies increases the sensitivity and specificity of the electrodiagnostic test.[4] The study is also unclear as to whether the author utilized and adhered to the AANEM standard nerve conduction protocol guidelines.

The author noted other limitations in his study. The study was based in a tertiary care center and thus may not have had a patient sample representative of a typical community patient population. A hand therapist was used as a substitute for a primary care physician to perform the majority of the testing using the CTS-6 assessment tool. Also, a technician performed the nerve conduction studies instead of a physician.

The author received funding from the Research Advisory Council of the Workplace Safety and Insurance Board for this study.

Abstract

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