An outcome measure of functionality in patients with lumber spinal stenosis: a validation study of the Iranian version of Neurogenic Claudication Outcome Score (NCOS)

BACKGROUND Neurogenic claudication (NC) is a common symptom in patients with lumbar spinal stenosis (LSS). The Neurogenic Claudication Outcome Score (NCOS) is a very short instrument for measuring functional status in these patients. This study aimed to translate and validate the NCOS in Iran. METHODS This was a prospective clinical validation study. The 'forward-backward' procedure was applied to translate the NCOS from English into Persian (Iranian language). A total of 84 patients with NC were asked to respond to the questionnaire at two points in time: at preoperative and at postoperative (6 months follow-up) assessments. The Oswestry Disabiltiy Index (ODI) also was completed for patients. To test reliability, the internal consistency was assessed by Cronbach's alpha coefficient. Validity was evaluated using known groups comparison and criterion validity (convergent validity). Internal responsiveness of the NCOS to the clinical intervention (surgery) also was assessed comparing patients' pre- and postoperative scores. RESULTS The Cronbach's alpha coefficients for the NCOS at preoperative and postoperative assessments were 0.77 and 0.91, respectively. Known groups analysis showed satisfactory results. The instrument discriminated well between sub-groups of patients who differed in claudication distance as measured by the Self-Paced Walking Test (SPWT). The change in the ODI after surgery was strongly correlated with change in the NCOS, lending support to its good convergent validity (r = 0.81; P < 0.001). Further analysis also indicated that the questionnaire was responsive to the clinical intervention (surgery) as expected (P < 0.0001). CONCLUSION In general, the Iranian version of the NCOS performed well and the findings suggest that it is a reliable and valid measure of functionality in patients with lumbar spinal stenosis who are suffering from neurogenic claudication.