(188) Development of a novel human pain model: a robust and reproducible pinprick methodology to evaluate cutaneous pain sensitivity

Abstract

Quantitative assessment of pain is a well-known challenge due to the complexity of the pain experience. The aim of our study was to develop a novel robust pinprick method to rapidly assess cutaneous pain sensitivity, and overcome limitations of previous models. Weighted pinprick devices (16 to 1024 mN) were used to quantitatively assess pain in 100 healthy males. Subjects verbally rated their pain using a numerical rating scale (NRS) from 1 to 10 where 1 = light touch and 10 = sharp pain. There was a log2 linear relationship between force and pain score, and repetition of this test 2 to 14 days later demonstrated within-subject pain sensitivity was remarkably consistent (p=0.16). This test allowed standardization of baseline pain by using, for each subject, the pinprick force required to elicit an NRS of 5-7. The test could also be used to enrich the study group by including only those with good baseline pain sensitivity. A series of 6 pinpricks were then performed in 4 areas on the forearms. Between-subject mean pain scores were normally distributed and there was no significant difference between the 4 areas (mean NRS 5.1-5.5, p=0.49). The three trained staff performing the tests contributed minimally to data variability (<4%, p=0.16). Using the variability of the data obtained in this study, we estimated the sample size required to evaluate the efficacy of topical analgesics in subsequent studies. The calculations showed that, using this paired study design, a statistically significant effect size of 1 NRS (p<0.05, 80% power) could be demonstrated using a sample size of 30 subjects. We present a robust and reproducible model to assess cutaneous analgesia in clinical settings and in early drug development programs.