Accuracy of Ultrasonography and Electromyography in the Diagnosis of Carpal Tunnel Syndrome

Carpal tunnel syndrome (CTS) is characterized by median nerve compression at the level of the wrist. It represents 90% of compressive neuropathies and is the most common upper member. For being a major cause of disability in hands, the early and accurate diagnosis to obtain a definitive treatment in CTS is essential. Despite this, there is no consensus on which is the most effective diagnostic criteria for CTS. The absence of a reference standard universally accepted for the diagnosis of CTS contributes to this scenario.

Ultrasonography (US) and electromyography (EMG) are the complementary examinations most often used in the diagnosis of CTS, but overestimated in their performance and require caution in interpreting the results, particularly the lack of a consensus on the ideal cutoff point for considering the diagnosis of CTS. This results in a wide variation in results of sensitivity and specificity for these tests, both the EMG (sensitivity = 82 to 98% and specificity = 19 to 88%) and for the US (sensitivity = 70 to 98% and specificity = 63 to 100%), in addition to a high proportion (20-40%) of false-negative and false-positive.

Most diagnostic accuracy studies at CTS compare the results of the US with EMG, considering most of the time the EMG as reference standard. There are few studies comparing the results of the US and EMG using other benchmarks, such as the degree of clinical improvement after surgical treatment of CTS or a combination of clinical signs and symptoms. The value of diagnostic tests for CTS can be established by comparing the diagnostic strategies and studying how they can affect the likelihood of STC. This spectrum can be considered the results of surgical treatment as the reference standard, as these are directly related to the diagnosis of CTS. Surgical treatment by classical open surgery is the definitive treatment of CTS and provides relief from symptoms, mainly the remission of paresthesia, with satisfactory results in up to 98% of the cases. The discomfort caused by paresthesia in the quality of life of patients and impairs daily manual activities and the quality of sleep is considerable in CTS. The remission of paresthesia is a clinical improvement parameter of the disease being an expected and relevant outcome for the patient. Primary and well-designed controlled studies with good methodological quality to guide the diagnostic practices and evaluate their effectiveness in an integrated manner in carpal tunnel syndrome (CTS) are unusual and challenging in the current literature. This study, innovative in its method has as primary objective to compare the accuracy of ultrasonography in relation electromyography in the diagnosis of carpal tunnel syndrome, using to the results of the surgical treatment as the reference standard.

The study design is a clinical trial of accuracy, primary, longitudinal, controlled, prospective, and performed in a single center. This clinical trial follows the accuracy STARD recommendations (Standards for Reporting of Diagnostic Accuracy).

Patients with clinical suspicion of CTS, who were referred and attended consecutively in our specialty clinic in hand surgery, were submitted to an initial clinical evaluation (ACI), by a same specialist in hand surgery, who used the CTS-6 clinical diagnostic instrument of GRAHAM et al. (2006), represented by a logistic regression model that estimates the diagnostic probability of CTS based on the presence or absence of the 6 diagnostic criteria that are: paresthesia, night paresthesia, weakness and/or atrophy thenar musculature, Tinel signal, Phalen test and loss of 2-points discrimination.