Clinical classification criteria for neurogenic claudication caused by lumbar spinal stenosis. The N-CLASS criteria

Abstract

Background Context Since imaging findings of lumbar spinal stenosis (LSS) may not be associated with symptoms, clinical classification criteria based on patient symptoms and physical examination findings are needed. Purpose To develop clinical classification criteria that identify patients with neurogenic claudication (NC) caused by LSS. Study Design Two stage process. Phase 1: Delphi process; Phase 2: cross-sectional study. Patient Sample Outpatients recruited from spine clinics in 5 countries. Outcome Measure Items from history and physical examination. Methods Phase 1: A list of potential predictors of NC caused by LSS was based on the available literature and evaluated through a Delphi process involving seventeen spine specialists (surgeons and non-surgeons) from 8 countries. Phase 2: Nineteen different clinical spine specialists from 5 countries identified patients they classified as having: 1) NC caused by LSS 2) Radicular pain caused by lumbar disc herniation (LDH), or 3) non-specific low back pain (NSLBP) with radiating leg pain. Patients completed survey items and specialists documented examination signs. Coefficients from General Estimating Equation models were used to select predictors, generate a clinical classification score and obtain a receiver operating characteristic (ROC) curve. Conduction of the Delphi process, data management and statistical analysis were partially supported by an unrestricted grant of less than 15000 US dollars from Merck Sharp and Dohme. No fees were allocated to participating spine specialists. Results Phase 1 generated a final list of 46 items related to LSS. In phase 2, 209 patients with leg pain caused by LSS (n=63), LDH (n=89) or NSLBP (n=57) were included. Criteria which independently predicted NC (p<0.05) were: age over 60; positive 30 second extension test; negative straight leg test; pain in both legs; leg pain relieved by sitting, and leg pain decreased by leaning forward or flexing the spine. A classification score using a weighted set of these criteria was developed. The proposed N-CLASS score ranged from 0 to 19, had an area under the curve of 0.92, and the cutoff (>10/19) to obtain a specificity of >90.0% resulted in a sensitivity of 82.0%. Conclusion Clinical criteria independently associated with neurogenic claudication due to LSS were identified. Use of these symptom and physical variables as a classification score for clinical research could improve homogeneity among enrolled patients.