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Thirty patients were treated with a flashlamp-pumped pulsed dye laser, with 0.45 ms pulse width and 585 nm wavelength. Punch biopsies were taken prior to treatment, and the biopsies were examined morphometrically. Three different test sites were exposed to laser light of fluence 5.25, 6.50 and 7.75 J/cm2. The degree of blanching was examined 6-8 weeks after treatment, and each site was retreated four times. Six patients (20%) achieved poor blanching, eight patients (27%) obtained moderate lightening and 16 patients (53%) showed good response. The vessels of the good responders were located significantly more superficially than the vessels of the moderate and poor responders (P < 0.05). The poor responders had significantly smaller vessels than the moderate and good responders (P < 0.01). The moderate responders had deeper, but larger vessels, than the poor responders. Hence, an increasing vessel diameter reduces the negative outcome of increasing vessel depth. The vessel diameter was correlated to the colour (P < 0.01), e.g. the mean vessel diameter was increasing from 16.5 microns in pink lesions to 51.2 microns in purple lesions. The vessel depth was partly reflected in the lesional colour, as the pink and purple lesions had significantly deeper vessels than the red ones (P = 0.02). These results indicate that pink lesions predict poor blanching due to deeply located small vessels, while red lesions predict a good therapeutic result because of more superficially located vessels.

We investigated the occurrence of pigmentary changes after flash lamp pumped dye laser treatment in 125 Norwegian patients. Post-treatment hyperpigmentation occurred with equal frequency during summer and winter (23%), and the facial regions did not exhibit higher occurrence than lesions located elsewhere. The patients that achieved hyperpigmented skin were not exposed to any higher fluence than those without this complication. On the contrary, we found that during the summer period from April to September the patients with post-treatment hyperpigmentation had been exposed to a significantly lower dose than those without pigmentary changes. These results indicate that the epidermal melanin content is not the only criterion for obtaining post-treatment hyperpigmentation. There might also be a constitutional disposition. In predisposed individuals the threshold dose for hyperpigmentation might be reduced in summer when the skin is more pigmented.