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.
Key words
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Article info
Publication history
Published online: March 08, 2017
Accepted:
January 31,
2017
Received:
October 4,
2016
Footnotes
No benefits in any form have been received or will be received related directly or indirectly to the subject of this article.
Identification
Copyright
© 2017 by the American Society for Surgery of the Hand. All rights reserved.
