Cutaneous side effects from laser treatment of the skin: skin cancer, scars, wounds, pigmentary changes, and purpura--use of pulsed dye laser, copper vapor laser, and argon laser.
Authors: Haedersdal M. 
Published: May 2023

It has been the intention of this thesis to increase the knowledge on the development of cutaneous side effects from treatment with the argon laser, the copper vapor laser, and the pulsed dye laser, which represent technical developments within laser systems used for treatment of vascular lesions. To reach that goal, the investigations focused on patient and lesional characteristics (skin pigmentation, skin redness, and epidermal thickness) and on the importance of UV irradiation before and after dermatological laser treatment. The aspect of UV irradiation was added because vascular lesions frequently involve the face and, therefore, may be exposed to sunlight in relation to laser treatment. Risk assessments were performed on clinically visible side effects in order to improve the preoperative information to the patients about their individual risks of obtaining side effects from dermatological laser treatment. The laser-induced side effects were evaluated by systematic clinical assessments, by histological and biochemical examinations, by skin reflectance measurements, optical profilometry, and ultrasonography. The term side effects is associated with both transient and permanent skin reactions such as purpura, wounds, textural changes, scars, pigmentary changes, and squamous cell carcinomas. Lightly pigmented, hairless hr/hr C3H/Tif mice, hairless, albino hr/hr MORO/Ibm mice, human, healthy volunteers, and children with port-wine stains were included in the studies. This thesis represents the first systematic and experimental approach to selected side effects from laser treatment of the skin. The argon laser (AL) and the copper vapor laser (CVL) The results from AL and CVL treatments are described together because these lasers are continuous/quasicontinuous lasers that do not meet the requirements for selective photothermolysis, which represents the most selective delivery of energy to cutaneous vessels. In normal-skinned human volunteers, the postoperative development of scars and pigmentary alterations depended on the preoperative constitutive skin pigmentation degree. Significant correlations were found between the preoperative skin pigmentation and the clinically scored pigmentary changes and scarring 1, 2, and 6 months postoperatively, indicating that dark-pigmented skin types respond with more heavy skin reactions than fair-pigmented skin types. Pigmentary changes occurred at lower intensity levels than scarring. No difference was seen between the AL and the CVL concerning the risk of inducing these side effects. In hairless, albino hr/hr MORO/Ibm mice increasing epidermal thicknesses reduced CVL-induced wounds and scars. Significant negative correlations were found between preoperative epidermal thicknesses and CVL-induced skin reactions. In lightly pigmented, hairless hr/hr C3H/Tif mice, CVL treatment induced an increase in skin pigmentation, evaluated by a semiquantitative technique. Postoperative UV irradiations with simulated solar UV increased the CVL-induced skin pigmentation additionally. The size of CVL-induced wounds and scars tended to enlarge by preoperative UV irradiations. In contrast, CVL-induced wounds were diminished and had a prolonged wound healing time when postoperative UV irradiations were given. This may indicate a deep constricted skin damage. Moreover, the histologically evaluated fibrosis and the frequency of bulging infiltration were increased by postoperative UV irradiation. When taking the liberty to extend the obtained results from the animal studies to humans, these results support the importance of pre- and postoperative sunprotection. Regarding skin cancer, in hairless mice it was found that one treatment with the CVL did not have a malignant potential itself. Pretreatment with the CVL at the highest intensity level (1.4W) delayed UV-induced photocarcinogenesis significantly. The pulsed dye laser (PDL) The PDL is described separately because it is the only laser in this thesis that fulf.