Stimulus Intensity For Measuring Temporal Summation Of Second Pain: The Case-Control Study Of Patients With Chronic Pain And Healthy Individuals

Abstract

Background: Central sensitization (CS) of the nociceptive system is linked to a disparity between the perceived pain intensity and the severity of the tissue damage in many chronic pain conditions. Temporal summation of second pain (TSSP) has been suggested as a psychophysical index for CS. However, there is no golden standard for protocols to measure TSSP. The purpose was to establish the stimulus intensity for measuring TSSP to obtain the best assessment of CS in healthy individuals and patients with chronic pain. Methods: Women patients with chronic myofascial temporomandibular disorders pain (n = 16) and healthy women volunteers with no pain (n = 15) participated. First, TSSP response patterns in healthy volunteers with no pain were tested. Second, differences in TSSP between groups were investigated. Pain thresholds (PT °C) were measured, and repetitive heat stimuli at three stimulus intensities (PT °C, PT+1 °C, PT+2 °C) were applied. TSSP parameters were quantified as TSSP magnitude (TSm), TSSP frequency (TSf). Generalized linear mixed-effect models with repetitive stimuli on pain ratings were conducted. Results: In healthy women volunteers, pain ratings significantly decreased at PT ℃ (P < .050), besides TSm and TSf at PT+2 ℃ were significantly higher than those at PT ℃ (P < .025). In chronic pain patients, pain ratings significantly increased at PT+1 ℃ and PT+2 ℃ (P < .050). At PT+2 ℃, TSm and TSf in chronic pain patients were significantly higher than healthy volunteers (P < .050). Conclusion: The stimulus intensity should be individually adjusted to 2 ℃ above the patient’s pain thresholds to assess TSSP clearly.