The study was conducted in a cross-sectional, observational, research design with two weeks and three months follow up to study the clinimetric quality (i.e. reliability and validity) of the Pain
DETECT. This study, to detect a NePC in patients suffering from chronic pain, was approved by the medical and ethical review board Committee on Research Involving Human Subjects region Arnhem-Nijmegen, Nijmegen, the Netherlands, Dossier number: 2008/348; NL 25343.091.08 and conducted in accordance with the declaration of Helsinki and the declaration of the World Medical Association. As required, written informed consent was obtained from patients prior to study participation. The protocol is registered in the Dutch National Trial Register: NTR 3030. The Pain
DETECT was translated and cross-culturally adapted into the Dutch language (Pain
DETECT -Dlv) (© Pfizer Pharma GmbH 2005, Pfizer bv 2008. Cappelle a/d IJssel, the Netherlands) in a separate study [
24] before the commencement of the present validation study. In this study, the same methodology was used as in the previously published protocol [
25] and as employed in a simultaneous study regarding the validity of the DN4 [
26] .
Patients
The patients were recruited from October 2009 until July 2013. Multicenter recruitment took place in the Netherlands in three academic centers specialized in pain medicine, three non-academic centers specialized in pain medicine and one non-academic department of neurology. The question to participate in the study was asked by the patients’ own physician. At that moment they only had a provisional diagnosis: LBLP, NSA pain or pain due to a suspected PND (Conditions associated with a lesion of the peripheral somatosensory system). These three groups of patients include a majority of the patients referred towards an academic or peripheral pain clinic from the general practitioner. Patients had to be diagnosed for the initial cause of the pain as classified according to the International Statistical Classification of Diseases and Related Health Problems 10th Revision (ICD-10)-2015-WHO Version 2015 [
27]. Importantly, patients were not pre-stratified on the target outcome: the existence of NePC yes or no [
28]. Patients, when willing to participate, were included when they met the following inclusion criteria: Male or female adult patients (> 18 years of age) with chronic (≥3 months) LBLP or NSA pain radiating into leg (s) or arm (s) respectively or patients with chronic pain due to a suspected PND. Exclusion criteria were
: Patients diagnosed with an active malignant disorder, compression fractures, patients with diffuse pains (pains with an origin in muscles, bones or joints: such as fibromyalgia or ankylosing spondylitis), severe mental illness, chronic alcoholism or substance abuse, inability to fill in the questionnaire adequately or incapable of understanding the Dutch language.
Physicians’ assessment
Patients were examined for the presence of NePC by two physicians which was considered to be the “gold standard” in this study. The physicians (pain specialists, pain specialist in training or neurologists always operated in differently composed pairs) worked independently from each other and were blinded to the classification made by the other physician. The physicians were not selected on basis of age, years of experience as a physician or other criteria. A full medical history was taken followed by a thorough clinical examination. A bedside examination (touch, pin prick, pressure, cold, heat and temporal summation) to assess patients’ pain [
25] was based on the European Federation of Neurological Societies (EFNS) guidelines [
29,
30], the IASP Neuropathic Pain Special Interest Group (NeuPSIG) guidelines on neuropathic pain assessment [
6] and the guidelines for assessment of neuropathic pain in primary care [
7]. Patients’ pain was classified by the physician as pain with present- or absent-NePC. The NeuPSIG Grading System for neuropathic pain as proposed by Treede et al. [
31] was used as a secondary comparison with the outcome of the Pain
DETECT-Dlv. The assessment of the Grading System was implemented in the standardized assessment protocol and thus included in the diagnostic work-up of the patients [
25]. The outcomes “probable” and “definite” were regarded as “present-NePC”. “Unlikely” and “possible” were rated as “absent-NePC” [
32‐
34]. All participating physicians underwent standard medical training, belonging to the classic medical curriculum, and examination of the (central) nervous system in particular. To achieve standardization of history and assessment of NePC presence in patients included in this study all participating physicians underwent a training in the performance of the clinical examination of the patients (including sensory (bedside) examination and use of the NeupSIG Grading System) [
25]. Training of the physicians took place at the participating center. During the execution of the study, the study coordinator (HT) visited the participating centers on a regularly basis to answer questions, to see if the necessary equipment was always available and to keep an eye on the inclusion of patients. Based on the order of assessment, the physician who performed the first assessment was called physician A and the physician who performed the assessment as a second physician was named physician B. However, the order of the physicians was based on availability during the study.
PainDETECT-Dlv and other questionnaires
The Pain
DETECT-Dlv (© Pfizer Pharma GmbH 2005, Pfizer bv 2008. Cappelle a/d IJssel, the Netherlands) [
2,
24] was designed as a simple, patient self-administered screening tool to screen for the presence of neuropathic pain without physical examination. This instrument consists of one item about the pain course pattern, one about radiating pain and seven items about the gradation of pain. An overall score is generated and ranges between − 1 and 38. Additionally, there are three items about pain severity (current, worst and average pain) included in the Pain
DETECT. For the original German version [
2] the outcome was as follows: ‘-1 - 12: negative’, neuropathic pain is unlikely; 13–18: ‘unclear’; result is ambiguous, however neuropathic pain can be present; 19–38 ‘positive’, neuropathic pain is likely.
The patient completed five questionnaires (including the Pain
DETECT-Dlv directly after the clinical assessment by the participating physicians but without any interference by the physicians. The researcher (HT) was available for help via telephone or in person when it was not clear how to fill in the questionnaires. Besides screening for NePC via the Pain
DETECT-Dlv [
24], the disability of the patient was assessed via the Disability Rating Index (DRI) [
35]. The existence of an anxiety disorder and/or depression were assessed via the Hospital Anxiety Depression Scale (HADS) [
36‐
38] and the Pain Attribution Scale (PAS) was used to assess patients attribution of his or hers pain. Quality of life was determined via the RAND 36-item Health Survey (RAND-36) [
39‐
41]. Two weeks and three months after the initial visit the follow-up questionnaires (the Patients Global Impression of Change (PGIC) [
42‐
44] and the Pain
DETECT-Dlv) were sent to the patient by mail.
Data
All data gathered from patients and physicians was collected on paper and stored at the Radboudumc, Nijmegen, The Netherlands. Data management and monitoring were performed within MACRO (MACRO, version 4.1.1.3720, Infermed, London, United Kingdom).
Statistical methods
Power calculation for this study was based on a expected NePC prevalence of 37% in an unselected cohort of patients with chronic low back pain [
2]. Sensitivity and specificity of the Pain
DETECT were assessed in the original validation study as respectively 85 and 80% [
2]. The sensitivity and specificity of the Pain
DETECT-Dlv was, on forehand, expected to be 80% with a prevalence of 37%. The lower 95% confidence limit was required to be > 0.55. According to the calculations following the formulas by Flahault et al. [
45] 132 patients with LBLP, NSA pain or suspected PND pain were needed so that the sample size contained a sufficient numbers of cases and controls [
25].
Qualitative variables were presented as frequencies and percentages. The quantitative variables were presented as mean and standard deviation (SD) or as median and inter quartile range (IQR). Based on the classifications of the two physicians, all patients were categorized as absent-NePC, NePC or ‘undetermined’ (i.e. the classification by both physicians jointly was not equal).
One-way ANOVA (with additional Tukey’s studentized range post-hoc test) or Kruskal-Wallis test were used to study differences between the three groups (NePC, absent-NePC, Undetermined).
Intraclass correlation (ICC) was used to assess reproducibility (‘test-retest reliability’) of the PainDETECT-Dlv between the fixed time points (baseline versus two weeks & baseline versus three months). The ICC and responsiveness of the PainDETECT-Dlv were assessed between each point of measurement.
A receiver operating characteristic (ROC) curve was calculated and the area under the curve (AUC) with 95% confidence interval is presented to indicate the discriminatory power of the Pain
DETECT-Dlv to discriminate patients classified as with or without a NePC. The classification was based on the physicians’ assessment outcome or based on the Grading System outcome, respectively. The theoretical maximum of the AUC is 100%, indicating a perfect discrimination and 50% is equal to tossing a coin. The optimal cut-off point of the Pain
DETECT-Dlv – sum score was calculated under the condition of equal-costs of misclassification, using the Youden-index. Sensitivity, specificity, positive and negative predictive values and the likelihood ratio in the population in this study was calculated at this cut-off point. Also, the ‘number needed to diagnose (NND)’ was assessed [
46] by use of the formula: NND = 1/[Sensitivity – (1-specificity)]. A clinical screening tool for the demonstration of a neuropathic pain component is considered valid if it has a high sensitivity, specificity and a high positive predictive value. For the measurement of the usefulness of the screening tool the likelihood ratio will be used [
47].
The agreement between the pain classification by the physicians, the NeuPSIG Grading Systems and the Pain
DETECT-Dlv (yes: ≥11, no:< 11) outcome was evaluated by using Cohen’s kappa (
K), prevalence index (P
i) and percentage of pair wise agreement (PA) [
25]. A
Κ ≥ 0.40 and a PA ≥ 70% is considered indicative of interobserver reliability which is acceptable for use in clinical practice [
48].
Data analysis and statistics were performed by use of Statistical Package for the Social Sciences (SPSS version 20.0, SPSS Inc., Chicago, Illinois, USA). Two-tailed p-value below 0.05 was considered statistically significant.