Spinal Cord Injury Pain Instrument and painDETECT questionnaire: Convergent construct validity in individuals with Spinal Cord Injury

Abstract

Background: Neuropathic pain (NeuP) is a frequent sequel of spinal cord injury (SCI). The SCI Pain Instrument (SCIPI) was developed as a SCI-specific NeuP screening tool. A preliminary validation reported encouraging results requiring further evaluation in terms of psychometric properties. The painDETECT questionnaire (PDQ), a commonly applied NeuP assessment tool, was primarily validated in German, but not specifically developed for SCI and not yet validated according to current diagnostic guidelines. We aimed to provide convergent construct validity and to identify the optimal item combination for the SCIPI. The PDQ was re-evaluated according to current guidelines with respect to SCI-related NeuP.

Methods: Prospective monocentric study. Subjects received a neurological examination according to the International Standards for Neurological Classification of SCI. After linguistic validation of the SCIPI, the IASP-grading system served as reference to diagnose NeuP, accompanied by the PDQ after its re-evaluation as binary classifier. Statistics were evaluated through ROC-analysis, with the area under the ROC curve (AUROC) as optimality criterion. The SCIPI was refined by systematic item permutation.

Results: Eighty-eight individuals were assessed with the German SCIPI. Of 127 possible combinations, a 4-item-SCIPI (cut-off-score = 1.5/sensitivity = 0.864/specificity = 0.839) was identified as most reasonable. The SCIPI showed a strong correlation (r_sp = 0.76) with PDQ. ROC-analysis of SCIPI/PDQ (AUROC = 0.877) revealed comparable results to SCIPI/IASP (AUROC = 0.916). ROC-analysis of PDQ/IASP delivered a score threshold of 10.5 (sensitivity = 0.727/specificity = 0.903).

Conclusion: The SCIPI is a valid easy-to-apply NeuP screening tool in SCI. The PDQ is recommended as complementary NeuP assessment tool in SCI, e.g. to monitor pain severity and/or its time-dependent course.

Significance: In SCI-related pain, both SCIPI and PainDETECT show strong convergent construct validity versus the current IASP-grading system. SCIPI is now optimized from a 7-item to an easy-to-apply 4-item screening tool in German and English. We provided evidence that the scope for PainDETECT can be expanded to individuals with SCI.