Determinants of thermal pain thresholds in normal subjects

OBJECTIVE Measurement of thermal pain thresholds is an essential part of quantitative sensory testing (QST). However, databases of QST show limitations due to large inter-individual variations including unreasonably low thresholds for thermal pain, lack of data on intra-individual variations over time and on the subjects' perception at threshold. This study sought to reduce inter-individual variations, investigated the reproducibility of measurements of thermal pain thresholds and included evaluation of thermally induced perceptions. METHODS Thermal pain thresholds were investigated in 20 healthy subjects over three weeks using two protocols, one of which differed in making the subjects familiar with the likely range of applied temperatures beforehand. Both protocols included subjective ratings of pain and temperature perception at the pain thresholds. RESULTS Data obtain using both protocols showed large inter-individual variations, but small intra-individual variations of pain thresholds over time as well as good feasibility and reproducibility of subjects' ratings at threshold. CONCLUSIONS Previous experience of test stimuli has no influence on the variability of thermal pain thresholds. However, measurement of thermal pain thresholds showed good reproducibility over time. Evaluation of perception at thresholds provided further reproducible data. SIGNIFICANCE Further approaches are needed to reduce variability of thermal pain thresholds; however, good reproducibility of thermal pain thresholds and thermally induced perceptions warrants consideration of their use in larger longitudinal studies.

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