Short-Term Histologic Effects of Nonablative Resurfacing: Results with a Dynamically Cooled Millisecond-Domain 1320 nm Nd:YAG Laser

BACKGROUND: It is widely believed that nonablative laser techniques can lead to dermal collagen remodeling without the obvious epidermal injury and the wound created with ablative approaches. This occurs when dermal collagen injury is induced without visible injury to the overlying epidermis. OBJECTIVE: To examine the acute histologic effects both 1 hour and several days after standardized treatment protocols of dynamically cooled millisecond domain Nd:YAG 1320 nm laser to provide further insight into the mechanism of action of nonablative resurfacing. METHODS: Multiple adjacent sites on the preauricular area of the cheek of 10 patients were biopsied following one to three laser passes of dynamically cooled millisecond-domain Nd:YAG 1320 nm laser. Biopsies were performed at 1 hour and at 3 days following a single treatment. The number of passes was varied from one to three and Tmax (peak temperature measured by integrated radiometer) during treatment was targeted for 45-48 degree C. RESULTS: At 1 hour after treatment, epidermal spongiosis and edema of the basal cell layer were present in all the specimens treated with three passes. At 3 days the three pass samples also showed microthrombosis, widened vessels, sclerosis of the vessel walls, and infiltration of neurophilic granulocytes. The occurrence of these histologic findings correlated well with the presence of clinical improvement (judged by photographs) at 8 weeks after treatment. Acute histologic changes and clinical improvement were not observed below treatment temperatures of Tmax 45 degree C or after one pass alone. Repeated temperatures above a Tmax of 48 degree C incurred risk of epidermal injury. CONCLUSION: Even though longer-term histologic findings have confirmed the collagen synthesis component of 1320 nm Nd:YAG laser, our data indicate that there may be some additional factors other than dermal collagen heating with subsequent collagen repair. The concept of true "nonablative resurfacing" may involve some form of subclinical epidermal injury that improves the clinical outcome. Acute changes involving superficial blood vessel injury with cytokine release may also be implicated. Our histologic findings suggest that three passes with fluence and cooling adjusted to a Tmax of 45 degree C-48 degree C yields improved clinical results.