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The Scratch Collapse Test and Evaluation of Patients with Coincident Carpal and Cubital Tunnel Syndrome
Justin Koh, BA, MA; Kodi K. Azari, MD, FACS; Prosper Benhaim, MD
UCLA, Los Angeles, CA

Introduction: Coincident ulnar compression at the cubital tunnel can coexist with carpal tunnel syndrome, but poses a diagnostic challenge - sensitivity of “gold standard” nerve conduction study results is limited to 60-70%. The Scratch Collapse Test is a somewhat controversial provocative diagnostic tool for cubital tunnel syndrome, but given its strong performance in the hands of experienced practitioners, it may be an excellent adjunct for diagnosing coincident ulnar neuropathy at the elbow in carpal tunnel syndrome patients.
Methods: This team has previously reported the results of a retrospective analysis of 515 patients to characterize demographics, medical history, physical exam findings, and nerve conduction study results correlated with coincident carpal and cubital tunnel syndromes. This cohort included 96 patients who were also evaluated by the scratch collapse test for ulnar neuropathy at the elbow. This partial cohort was assessed for diagnostic sensitivity of the scratch collapse test. We modified an existing clinical scoring scheme to assess the relative clinical weight of the scratch collapse test. The original scoring scheme evaluated loss of intrinsic hand strength, ulnar sensation loss, positive elbow flexion test, positive cubital tunnel Tinel's sign, and abnormal ulnar nerve conduction study to evaluate risk for coincident compression neuropathy. All modified scoring schemes were assessed by receiver operator characteristics (ROC) curves, as well as by sensitivities, specificities, positive, and negative predictive values.
Results: Compared to other physical exam findings specific for cubital tunnel syndrome, the scratch collapse test outperformed all other tests, with a sensitivity of 78.69%. The original scoring model showed an ROC area under the curve (AUC) of 0.9295 with five equally-weighted components. Modified to include the scratch collapse test, this ROC AUC increased to 0.9618 (nearly a perfect predictor of coincident compression).
Conclusions: In addition to outperforming other diagnostic factors for evaluating cubital tunnel syndrome, the scratch collapse test significantly improved the holistic diagnostic evaluation of patients with coincident compression neuropathy. In this developmental cohort, a modified clinical score including the scratch collapse test was a robust and efficient method for diagnosing patients at risk for coincident carpal and cubital tunnel syndromes.

Figure 1. Comparison of Relative Sensitivities of Physical Exam Findings

Figure 1. Comparison of ROC curves for a.) Conventional score system and b.) Scratch-Collapse modified score system

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