Validity, reliability, and clinical importance of change in a 0-10 numeric rating scale measure of spasticity: A post hoc analysis of a randomized, double-blind, placebo-controlled trial

Background: The measurement of spasticity as a symptom of neurologic disease is an area of growing interest. Clinician-rated measures of spasticity purport to be objective but do not measure the patient's experience and may not be sensitive to changes that are meaningful to the patient. In a patient with clinical spasticity, the best judge of the perceived severity of the symptom is the patient. Objectives: The aim of this study was to assess the validity and reliability, and determine the clinical importance, of change on a 0-10 numeric rating scale (NRS) as a patient-rated measure of the perceived severity of spasticity. Methods: Using data from a large, randomized, doubleblind, placebo-controlled study of an endocannabinoid system modulator in patients with multiple sclerosisrelated spasticity, we evaluated the test-retest reliability and comparison-based validity of a patient-reported 0-10 NRS measure of spasticity severity with the Ashworth Scale and Spasm Frequency Scale. We estimated the level of change from baseline on the 0-10 NRS spasticity scale that constituted a clinically important difference (CID) and a minimal CID (MCID) as anchored to the patient's global impression of change (PGIC). Results: Data from a total of 189 patients were included in this assessment (114 women, 75 men; mean age, 49.1 years). The test-retest reliability analysis found an interclass correlation coefficient of 0.83 (P < 0.001) between 2 measures of the 0-10 NRS spasticity scores recorded over a 7- to 14-day period before randomization. A significant correlation was found between change on 0-10 NRS and change in the Spasm Frequency Scale (r = 0.63; P < 0.001), and a moderate correlation was found between the change on 0-10 NRS and the PGIC (r = 0.47; P < 0.001). A reduction of -30% in the spasticity 0-10 NRS score best represented the CID and a change of 18% the MCID. Conclusions: The measurement of the symptom of spasticity using a patient-rated 0-10 NRS was found to be both reliable and valid. The definitions of CID and MCID will facilitate the use of appropriate responder analyses and help clinicians interpret the significance of future results.