Secondary hyperalgesia to heat stimuli after burn injury in man

The aim of the study was to examine the presence of hyperalgesia to heat stimuli within the zone of secondary hyperalgesia to punctate mechanical stimuli. A burn was produced on the medial part of the non-dominant crus in 15 healthy volunteers with a 50×25 mm thermode (47°C, 7 min), and assessments were made 70 min and 40 min before, and 0, 1, and 2 h after the burn injury. Hyperalgesia to mechanical and heat stimuli were examined by von Frey hairs and contact thermodes (3.75 and 12.5 cm 2), and pain responses were rated with a visual analog scale (0–100). The area of secondary hyperalgesia to punctate stimuli was assessed with a rigid von Frey hair (462 mN). The heat pain responses to 45°C in 5 s (3.75 cm 2) were tested in the area just outside the burn, where the subjects developed secondary hyperalgesia, and on the lateral crus where no subject developed secondary hyperalgesia (control area). The burns decreased pain thresholds and increased pain responses to both thermal and mechanical stimuli within the burn ( P