Reliability of conditioned pain modulation for the assessment of endogenous pain control pathways

Introduction Conditioned pain modulation test paradigms are commonly used in humans for the convenient non-invasive testing of endogenous pain control pathways. In this context, interdigital web pinching has recently been proposed as a conditioning stimulus avoiding confounding with cardiovascular pain modulation effects. Reliability of this test paradigm has, however, not been sufficiently examined. The aim of this study was to examine inter-rater reliability of conditioned pain modulation assessment using interdigital web pinching. Methods Twenty healthy subjects were independently examined on two days by two different raters. The pressure pain threshold, measured at the thenar eminence of the dominant hand, served as the test stimulus before and after a two-minute period of conditioning using interdigital web pinching applied between the index and middle finger of the non-dominant hand. The intraclass-correlation-coefficient, coefficient of variation and standard error of measurement were calculated. Agreement was assessed using the Bland and Altman approach. Results The intraclass-correlation-coefficient and standard error of measurement of our conditioned pain modulation test paradigm was 0.76 and 1.6 N respectively. The limits of agreement were −6.4 to 5.6 N (mean difference −0.4 N). Discussion Our conditioned pain modulation test paradigm might be useful as an alternative method for the assessment of pain inhibitory pathways.