The Cervical Radiculopathy Impact Scale: development and evaluation of a new functional outcome measure for cervical radicular syndrome

Objective:To develop and validate an outcome scale for the cervical radicular syndrome and to build a mapping, predicting EQ-5D utility from the new scale. Study design and setting:An item pool was developed based on literature and patient and clinician interviews. Item selection was based on symptomatology, factor analysis, and internal consistency. We assessed: (a) test-retest reliability by standard error of measurement and intraclass correlation coefficients; (b) construct validity by testing 22 hypotheses on relationships with existing measures and known-group differences. For the mapping, performance was assessed by mean absolute error and root mean squared error. Results:A total of 254 patients with cervical radicular syndrome completed the first questionnaire, 61 stable patients a retest. Item selection led to a 21-item questionnaire consisting of three subscales: Symptoms, Energy and postures, and Actions and activities. Standard error of measurement values ranged from 6.7 to 11.2 on a 0 to 100 scale. All subscales showed good reliability (intraclass correlation coefficients: 0.84, 0.87, and 0.94). All hypotheses for construct validity were confirmed. A linear utility mapping was preferred, with reasonable statistical performance. Conclusion:We developed a reliable and valid cervical radicular syndrome specific outcome scale, called the Cervical Radiculopathy Impact Scale (CRIS). This new questionnaire may facilitate (cost-)effectiveness studies in this field.