Evaluation of the Scratch Collapse Test for Carpal and Cubital Tunnel Syndrome-A Prospective, Blinded Study

To clarify the sensitivity, specificity, and interrater reliability of the scratch collapse test for carpal tunnel syndrome (CTS) and cubital tunnel syndrome, using blinded observers in a general patient population.

Ninety-two subjects were recruited from all patients referred for electrodiagnostic studies for upper extremity symptoms that were thought to be related to an entrapment mononeuropathy. The scratch collapse test was performed twice on each patient, once by the resident and once by a nerve conduction technician. Both observers were blinded to all aspects of the patient's presentation. Sensitivity and specificity for the scratch collapse test were calculated twice, once using electrodiagnostic testing results and a second time using a validated clinical tool (the CTS-6) as the reference standard. The interrater reliability was also calculated.

Using electrodiagnostic criteria as a reference standard, the scratch collapse test had a sensitivity of 7% and a specificity of 78% for CTS. Using clinical criteria as a reference standard, the test had a sensitivity of 15% and a specificity of 87%. For cubital tunnel syndrome, the sensitivity was 10% and the specificity was 90%. For the resident/technician 1, kappa was -0.025 (worse than chance alone). For the resident/technician 2, kappa was 0.211 (fair strength of agreement).

The sensitivity of the scratch collapse test for CTS and cubital tunnel syndrome was lower than that found in other studies, regardless of whether a clinical or an electrodiagnostic reference standard was used. The specificity was high. Overall interrater agreement was lower than previously reported. These results call into question the sensitivity and interrater reliability of the scratch collapse test for CTS and cubital tunnel syndrome.

Diagnostic II.