Evaluation of variations in sensory and pain threshold assessments by electrocutaneous stimulation

Assessed sensory and pain thresholds can change consequently to disturbances associated with ongoing pain. Such assessments could be an additional method in the daily clinical evaluation of perceived pain. To study the test-retest variability within-day and between-day of such procedures a newly developed instrument producing electrocutaneous stimulation, PainMatcher (PM), was used to assess the electrical sensory thresholds (EST) and pain thresholds (EPT) in healthy volunteers and in patients with pain. The produced data were considered ordinal and analyzed with rank-invariant statistics with properties of analyzing systematic disagreement, bias, and individual variations. The percentage agreements within +/- 1PM value for EST were in the two groups of healthy volunteers and patients in pain 94% and 92%, and for EPT assessments 49% and 78%, respectively. The variability in the EST assessments is possibly explained by a slight bias while the individual variations were negligible between the two occasions. The assessed EPT were unbiased in both groups while individual variations were significant among the healthy volunteers but negligible among the patients in pain. The EST was found to be increased in pain patients compared to healthy volunteers, p < 0.03, and the EPT decreased in pain patients compared to healthy volunteers, p < 0.001. The results in this study indicate stable and reliable assessments of EST and EPT except for a possible bias. The threshold assessment procedure followed in this study may be a valuable tool in the clinical evaluation of sensory and pain assessments in pain patients.