Development of a clinical prediction rule for the diagnosis of carpal tunnel syndrome

OBJECTIVES: To develop a clinical prediction rule (CPR) and to assess the reliability and diagnostic accuracy of individual clinical examination items for the diagnosis of carpal tunnel syndrome (CTS). DESIGN: Prospective diagnostic test study with blind comparison to a reference criterion of a compatible clinical presentation and abnormal electrophysiologic findings. SETTING: Multicenter medical center and community hospital with patient referrals from ambulatory primary care and specialty practice settings. PARTICIPANTS: Eight-two consecutively referred patients (50% men; mean age, 45+/-12 y) with suspected cervical radiculopathy or CTS referred for electrophysiologic examination. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Sensitivity, specificity, and likelihood ratios. RESULTS: The CPR identified in this study consisted of 1 question (shaking hands for symptom relief), wrist-ratio index greater than .67, Symptom Severity Scale score greater than 1.9, reduced median sensory field of digit 1, and age greater than 45 years. The likelihood ratio for the CPR was 18.3 when all 5 tests were positive. Interrater reliability was acceptable for all but 2 clinical examination items. CONCLUSIONS: The CPR identified was more useful for the diagnosis of CTS than any single test item and resulted in posttest probability changes of up to 56%. Further investigation is required both to validate the test-item cluster and to improve point-estimate precision.