The validity of ex vivo laser skin treatment for histological analysis. A prospective controlled study.

[BACKGROUND] Laser treatment of skin following removal from human subjects has been the staple of laser research. However, no study has been done to assess the efficacy of ex vivo skin for predicting the behavior of laser treatments in living human tissue.

[OBJECTIVE] To assess the validity of the ex vivo model by comparing histological characteristics of skin treated with laser prior to and following its removal in rhytidectomy.

[STUDY DESIGN] Nonrandomized controlled intervention study in which each patient served as both experimental subject and control for different skin sites.

[PATIENTS] Ten patients with actinic skin changes.

[INTERVENTIONS] Patients underwent laser treatment to 4 left preauricular sites 1 hour prior to rhytidectomy as follows: carbon dioxide laser treatment alone, carbon dioxide laser treatment followed by erbium:YAG laser treatment, erbium:YAG laser treatment alone, and erbium:YAG laser treatment followed by carbon dioxide laser treatment. The skin was examined by a dermatopathologist blinded to the identity of each specimen. Untreated skin was also removed and immediately subjected to laser treatment identical to that employed in the in vivo skin. This skin was examined histologically.

[MAIN OUTCOME MEASURES] Regularity of ablation, depth of the necrotic zone, amount of skin removed, degree of collagen injury, and degree of inflammation.

[RESULTS] There were significant differences between the ex vivo and in vivo groups. The ex vivo specimens demonstrated more than 10 times the irregularity of ablation of the in vivo specimens (irregularity index of 3.0 for the ex vivo group vs 0.25 for the in vivo specimens; P < .05). The incidence of collagen injury was slightly lower for the ex vivo group (1.0 vs 1.3), as was the degree of inflammation (1.4 vs 1.5). The greatest differences were the significantly smaller necrotic zone in the ex vivo specimens (51 vs 71 microns) and the smaller amount of skin removed (118 vs 234 microns). These findings were consistent for all 4 laser treatment regimens studied.

[CONCLUSIONS] Significant differences were found between the in vivo and ex vivo models. Irregularity of ablation in the ex vivo specimens was 10 times that in the living specimens, limiting histological accuracy in the ex vivo model. The ex vivo skin model underestimated the amount of tissue ablation. This suggests that an in vivo model should be adopted as the standard for laser research.