The Effect of Combined Skin and Deep Tissue Inflammatory Pain Models

Cutaneous hyperalgesia is prominent in the ultraviolet-B (UVB) model of inflammatory pain. This study investigated possible interactions between cutaneous and deep tissues hyperalgesia.

A total of 16 healthy volunteers participated in the study. Skin inflammation was induced unilaterally by UVB irradiation (three times of the individual minimal erythema dose) in square-shaped areas on the upper-trapezius and lower-back. Moderate delayed onset muscle soreness (DOMS) was induced bilaterally in the low-back by eccentric exercise. Cutaneous blood flow, mechanical thresholds, pressure pain thresholds (PPTs), temporal summation to repetitive pressure stimulation, and stimulus-response functions (SR curve) relating graded pressure stimulations and pain intensity were measured within and outside the irradiated areas, before and 24 hours after irradiation and eccentric muscle exercise.

Compared with baseline (P < 0.05): the assessments 24 hours after irradiation demonstrated: 1) increased superficial blood flow inside and outside the irradiated areas and in the DOMS site; 2) reduced mechanical thresholds within the irradiated areas; 3) left-shifted SR curve function within and outside the irradiated areas; and 4) facilitated temporal summation of pain inside the irradiated areas and in the DOMS site. There was no significant influence of muscle hyperalgesia on skin measures in normal or UVB-inflamed skin.

Moderate degrees of muscle sensitization could not facilitate UVB-induced cutaneous mechanical sensitivity, whereas UVB-induced neurogenic inflammation is enhanced when the DOMS is present.