The pattern and time course of somatosensory changes in the human UVB sunburn model reveal the presence of peripheral and central sensitization

The ultraviolet B (UVB) sunburn model was characterized with a comprehensive battery of quantitative sensory testing (QST). Primary hyperalgesia in UVB-irradiated skin and secondary hyperalgesia in adjacent nonirradiated skin were studied in 22 healthy subjects 24 h after irradiation with UVB at 3-fold minimal erythema dose of a skin area 5 cm in diameter at the thigh and compared to mirror-image contralateral control areas. The time course of hyperalgesia over 96 h was studied in a subgroup of 12 subjects. Within the sunburn area, cold hyperesthesia (P = .01), profound generalized hyperalgesia to heat (P < .001), cold (P < .05), pinprick and pressure (P < .001), and mild dynamic mechanical allodynia (P < .001) were present. The finding of cold hyperalgesia and cold hyperesthesia is new in this model. The sunburn was surrounded by large areas of pinprick hyperalgesia (mean ± SEM, 218 ± 32 cm2) and a small rim of dynamic mechanical allodynia but no other sensory changes. Although of smaller magnitude, secondary hyperalgesia and dynamic mechanical allodynia adjacent to the UVB-irradiated area were statistically highly significant. Primary and secondary hyperalgesia developed in parallel within hours, peaked after 24-32 h, and lasted for more than 96 h. These data reveal that the UVB sunburn model activates a broad spectrum of peripheral and central sensitization mechanisms and hence is a useful human surrogate model to be used as a screening tool for target engagement in phases 1 and 2a of drug development.