Test–retest reliability of pain location using three different body chart grids: a study on healthy volunteers

Abstract

BACKGROUND. Pain location (PL) is a variable of interest in the assessment of patients with pain commonly investigated through the pain drawing (PD). PL is commonly considered to describe pain patterns in different pathological conditions, and to monitor the effectiveness of interventions. Despite this the reliability of PL has not yet been accurately explored. PL measurement consists in superimposing a grid on a body chart to identify which body regions were involved in the PD. Grids may include a different number of cells, with different shapes and dimension (e.g. anatomic regions, squares), thus affecting the PL resolution. Although it is reasonable that different grids lead to different PL measurements no studies on this issue were found, and it’s unclear whether a grid may be preferable to another. PURPOSE. The aim of the study was to investigate the PL test-retest reliability after a painful stimulus elicited by the upper limb neurodynamics test 1 (ULNT1) using three different body chart grids. METHODS. Forty healthy volunteers (27 females, 13 males) underwent an ULNT1 until the pain onset, and afterwards completed two consecutive PDs with an interval of one minute between. PDs were shaded with a stylus pen on an iPad® and processed using a custom designed software. PDs were assessed with three grids: G1 including 410000 pixels, G2 including 170 small-anatomical regions (e.g. fingers, hypothenar, thenar), and G3 including 34 macro-anatomical regions (e.g. hand, forearm, arm). The consistency of PLs for each couple of consecutive PDs was estimated using the Jaccard Similarity Coefficient (JSC). The proposed coefficient ranges from 0 to 1. When the JSC was equal to 1 PLs reported on two consecutive PDs was identical, while 0 corresponded to completely different PLs for two consecutive PDs. The PL test-retest reliability of the three grids was expressed as the median value of the JSC. A Friedman test was used to evaluate differences in JSC between different grids. Pairwise comparisons were performed using the Wilcoxon signed rank test for matched samples with a Bonferroni correction for multiple comparisons. RESULTS. The median value and range of the JSC were 0.73 (0.15 - 0.88) for G1, 0.91 (0.50 - 1.00) for G2, and 1.00 (0.50 – 1.00) for G3. The JSC calculated with different grids were statistically significantly different (p<0.05). Statistically significant differences in JSC were observed also between all pairwise comparisons (G1-G2, G1-G3, G2-G3) (p<0.0167). CONCLUSIONS. All the consecutive PDs although referred to the same painful stimulus showed some differences. The grids based on pixels were the more sensitive while macro-anatomic regions were less sensitive to differences in PD, giving the lower and the higher JSC respectively. All JSC were indicative of a high PL test-retest reliability. IMPLICATIONS. The choice of the grid for PL assessment should consider the resolution of PL that better suits the aim of the measurement. For very sensitive measurement of PL the pixel grid seems to be preferable. The accuracy and validity of PL reporting through PD needs to be further investigated.