Elsevier

The Spine Journal

Volume 18, Issue 6, June 2018, Pages 941-947
The Spine Journal

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

https://doi.org/10.1016/j.spinee.2017.10.003Get rights and content

Abstract

Background Context

Because 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

The objective of this study was to develop clinical classification criteria that identify patients with neurogenic claudication (NC) caused by LSS.

Study Design

This study is a two-stage process that includes Phase 1, the Delphi process, and Phase 2, the cross-sectional study.

Patient Sample

Outpatients were recruited from spine clinics in five countries.

Outcome Measure

The outcome measure includes items from the patients' history and physical examination.

Methods

In Phase 1, a list of potential predictors of NC caused by LSS was based on the available literature and was evaluated through a Delphi process involving 17 spine specialists (surgeons and non-surgeons) from eight countries. In Phase 2, 19 different clinical spine specialists from five 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. The patients completed survey items and the specialists documented the examination signs. Coefficients from general estimating equation models were used to select predictors, to generate a clinical classification score, and to obtain a receiver operating characteristic curve. Conduction of the Delphi process, data management, and statistical analysis were partially supported by an unrestricted grant of less than 15,000 US dollars from Merck Sharp & 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 that independently predicted NC (p<.05) were age over 60 years, 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 and 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%.

Conclusions

Clinical criteria independently associated with neurogenic claudication due to LSS were identified. The use of these symptom and physical variables as a classification score for clinical research could improve homogeneity among enrolled patients.

Introduction

Neurogenic claudication (NC), also called pseudoclaudication [1], [2], is the cardinal symptom caused by lumbar spinal stenosis (LSS) [3]. Lumbar spinal stenosis represents a degenerative process involving the narrowing of the spinal canal around the nerve roots of the cauda equina within the dural sac caused by facet joint osteoarthritis, hypertropic thickening and bulging of the ligamentum flavum, and bulging of the intervertebral disc [4]. Since the first descriptions of the relationship between symptoms of NC and radiographic images demonstrating LSS almost 70 years ago [1], [5], hundreds of scientific contributions have been published, including randomized controlled trials and clinical practice guidelines. A key limitation of the existing literature is the heterogeneity of eligibility criteria for identifying patients with symptoms caused by LSS [6]. On its own, the size of the spinal canal is not a valid diagnostic criterion; because there is no agreement on what defines “normal” and “stenotic,” stenotic images can be seen in asymptomatic subjects, and there is a limited correlation between anatomical findings and symptoms [7], [8]. Consequently, eligibility criteria vary across studies and limit their generalizability, compromising attempts to compare results [9]. These limitations have been recognized in proposals to develop consensus criteria to define and classify patients with symptomatic LSS [3], [10].

In the absence of specific biomarkers, the use of classification criteria is a key step to identify patients with a specific disease and to establish homogenous groups of patients for clinical or population studies, which is essential in multicenter studies and contributes to the generalizability of results [9], [11], [12], [13], [14]. For other musculoskeletal diseases (eg, rheumatoid arthritis, spondyloarthropathy), the widespread adoption of classification criteria has been a key factor spurring advances in diagnosis and treatment [11]. In the field of low back pain (LBP), prior attempts to differentiate patients with LBP with leg pain and neurologic signs from other categories of patients with LBP failed to define any specific diagnostic criteria for these categories [12].

In view of the large economic burden related to the management of LBP syndromes including LSS [13], there is a clear need to develop validated clinical classification criteria for research and clinical purposes [9]. During a workshop at the 11th Forum for Primary Care Research in Low Back Pain, a multidisciplinary, international study to develop classification criteria for LBP-related leg symptoms was conceived.

Section snippets

Methods

The present study was designed according to rules defined by Fries for constructing classification criteria [14] and focused on NC caused by LSS and radicular pain caused by lumbar disc herniation (LDH). Here, we report on the development and the validation of clinical classification criteria for NC caused by a LSS. Criteria for LDH have been previously reported [15].

Delphi process

The literature review and items identified by the group of spine specialists resulted in a list of 236 potential items for spine-related leg pain symptoms and physical examination findings. Out of the 236 items, 96 were associated with neurogenic claudication caused by LSS, whereas the others were associated with radicular pain caused by LDH. In the first round, 3 of the 96 items were excluded, all based on mean scores of <3, leaving 93 items. In the second round, 47 items were excluded. Of the

Discussion

Classification criteria are defined as a set of disease characteristics used to group individuals into a well-defined homogenous population with similar clinical disease features [23]. The use of classification criteria is advocated and promoted for classifying conditions that lack highly specific biomarkers [20], [23], [24]. The present study was conducted by a multidisciplinary international team of spine specialists using a modified Delphi process for item generation and a clinical

Conclusions

This international multidisciplinary study is the first to propose classification criteria for NC due to LSS. When designing future research studies on LSS, the use of the N-CLASS could improve the homogeneity of the studied populations and increase the quality of study comparisons and data pooling.

Acknowledgments

We express our gratitude to all spine specialists who participated in the Delphi process and in the recruitment of patients, as well as the patients who kindly participated. We also thank MSD for their financial support.

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    Author disclosures: SG: Nothing to disclose. DSC: Nothing to disclose. KK: Nothing to disclose. FMK: Nothing to disclose. MM: Nothing to disclose. JR: Nothing to disclose. MN: Nothing to disclose. JFK: TDC: Nothing to disclose. JNK: Nothing to disclose. SJA: Nothing to disclose.

    The disclosure key can be found on the Table of Contents and at www.TheSpineJournalOnline.com.

    This study received financial support from an unconditional scientific grant from MSD. MSD had no role in the study design, data collection, data analysis, data interpretation, or writing of the report. Publication of this study was not contingent upon approval from the study sponsor. No fees were allocated to participating spine specialists.

    None of the authors report any conflict of interest. The amount of support received for this study is approximately $1,001–$10,000.

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