American Society for Peripheral Nerve

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Evaluation of the Scratch Collapse Test for Carpal and Cubital Tunnel Syndrome A Prospective, Blinded Study
Kate Montgomery, MD; Gerald Wolff, MD, FRCPC; Kirsty U. Boyd, MD, FRCSC;
University of Ottawa, Ottawa, ON, Canada

Introduction: The scratch collapse test is a novel physical exam maneuver for compression neuropathy. In the 2008 paper by Cheng, the test out-performed other common physical exam maneuvers for carpal and cubital tunnel syndrome. Subsequent studies have not reproduced these findings. We sought to prospectively evaluate the sensitivity, specificity, and inter-rater reliability of the scratch collapse test for carpal and cubital tunnel syndrome using blinded observers.

Materials and Methods: Subjects were recruited from all patients referred for upper extremity nerve conduction studies for presumed mononeuropathy. The scratch collapse test was performed twice on each patient, once by the resident and once by one of the nerve conduction technicians. Both observers were blinded to all aspects of the patient's presentation. The sensitivity and specificity for the scratch collapse test were calculated twice, once using electrodiagnostic testing results as the reference standard and a second time using a validated clinical tool (The Carpal Tunnel Syndrome 6) as the reference standard. The inter-rater reliability was also determined.

Results: Using electrodiagnostic criteria as a reference standard, the scratch collapse test as performed by the resident had a sensitivity of 7% and a specificity of 78% for carpal tunnel syndrome (tech 1 had a sensitivity of 7% and a specificity of 94%). Using clinical criteria as a reference standard for carpal tunnel syndrome, the test as performed by the resident had a sensitivity of 15% and a specificity of 87%. For cubital tunnel syndrome, the sensitivity was 10% and the specificity was 90% (for tech 1, the sensitivity was 0% and the specificity was 99%). Kappa was -0.025 (worse than chance alone) for the resident/tech 1 and 0.211 (fair strength of agreement) for the resident/tech 2.

Conclusions: The sensitivity of the scratch collapse test for carpal and cubital tunnel syndrome was lower than that found in other studies, regardless of whether a clinical or an electrodiagnostic reference standard was used. Kappa ranged from worse than chance to fair, highlighting the operator-dependent nature of the maneuver. The strength of agreement overall was lower than previously reported. These results call into question the diagnostic utility of the scratch collapse test for entrapment mononeuropathies of the upper extremity.


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