The Accuracy of the Scratch Collapse Test Performed by Blinded Examiners on Patients With Suspected Carpal Tunnel Syndrome Assessed by Electrodiagnostic Studies

Abstract

Purpose: A diagnostic maneuver known as the "scratch-collapse test" (SCT), to aid in the diagnosis of compressive upper limb neuropathies such as carpal tunnel syndrome (CTS), has been described. There is a wide variability in the sensitivity and specificity values reported to date, and the reason for this discrepancy is unclear. The purpose of this study was to evaluate the utility of the SCT performed by examiners blinded to the meaning of the examination.

Methods: Forty consecutive patients referred to a single physiatrist for electrodiagnostic testing for the evaluation of suspected CTS were included in the study. The patients were evaluated by blinded physician examiners with no knowledge of the SCT. The examiners were instructed on the maneuver but were not told the purpose of the test or the significance of a "positive" or "negative" response. Routine electrodiagnostic testing including nerve conduction studies and electromyography were also performed.

Results: For the blinded examiners, the SCT had a sensitivity of 0.24, a specificity of 0.6, a positive predictive value of 0.73, a negative predictive value of 0.15, and the accuracy was 31%. The SCT performed by the attending physician demonstrated a sensitivity of 0.28, a specificity of 0.75, a positive predictive value of 0.81, a negative predictive value of 0.2, and the accuracy was 37%. All of the previous values are presented with electrodiagnostic studies as the reference standard for CTS. There was disagreement between the blinded, inexperienced examiners and the attending physician in only 3 of the 40 patients evaluated with the SCT.

Conclusions: The SCT appears to have low sensitivity and specificity values relative to electromyography findings in patients with CTS when performed by examiners blinded to the meaning of the patients' response. Further study of this maneuver is necessary to fully assess its performance.

Type of study/level of evidence: Diagnostic II.

Keywords: Carpal tunnel syndrome; provocative maneuvers; scratch collapse test.