Longitudinal and interventional pain studies require reliable outcome measures. Self-reported pain intensity and unpleasantness are gold standard pain assessment measures. Additionally, the extent of secondary hyperalgesia elicited by experimental pain reflects central sensitization. Together, these measures can serve as outcome measures for pain studies. Phasic heat pain (PHP) is an increasingly popular experimental stimulation paradigm. However, the stability and test-retest reliability of pain outcome measures from PHP across multiple sessions, on separate days remains unknown. Here, the test-retest reliability and stability of these pain outcome measures to PHP across three sessions at least two days apart were determined. Twenty-four healthy participants (12 males, 12 females) attended three sessions, each with a familiarization procedure and a PHP calibrated to 50/100 pain intensity. Pain intensity ratings, pain unpleasantness ratings and area of secondary hyperalgesia were measured after PHP. Intraclass correlation coefficients (ICC) showed that pain intensity ratings had good reliability (ICC =.755), pain unpleasantness ratings had moderate reliability (ICC =.636), and secondary hyperalgesia had good reliability (ICC =.840). A repeated-measures ANOVA revealed significant differences, and thus low stability, for self-report ratings across sessions (ps 01 = 3.36). Validation of the PHP pain intensity findings in an independent dataset demonstrated moderate reliability (ICC =.718). While all pain measures had moderate-to-good reliability, only secondary hyperalgesia area remained stable across sessions. PERSPECTIVE: This study demonstrates that outcome measures (pain intensity, pain unpleasantness and secondary hyperalgesia) for a PHP paradigm had moderate-to-good reliability, and only secondary hyperalgesia area was stable across sessions. These findings indicate the need for counterbalancing sessions and assessing multiple pain outcome measures in studies that capture individual differences.
Vera et al. (Sat,) studied this question.