Does imiquimod histologically rejuvenate ultraviolet radiation-damaged skin?

Imiquimod (IMI) 5% is believed by some to result in an improved cosmetic appearance of chronically ultraviolet radiation (UV)-damaged skin.

The objective was to determine what histologic and immunohistologic changes were present in actinically damaged skin after treatment with IMI.

Pre- and posttherapy biopsies of 12 patients with histories of actinic keratoses were evaluated with routine histology and immunohistochemical stains including p53, p63, proliferating cell nuclear antigen (PCNA), c-kit, and Factor XIIIa.

After IMI therapy there was less compact hyperkeratosis, a more uniform rete ridge pattern with a more ordered proliferation of the epidermis, and a decrease in sun-damaged melanocytes. The papillary dermis showed a more uniform cellularity, and there was increased cellularity within the area of solar elastosis. After therapy, staining for p53, p63, and PCNA was decreased within the epidermis; staining for c-kit was decreased but more uniform in the basal cell; and Factor XIIIa expression was increased within the papillary dermis with a more ordered pattern of staining.

These morphologic and immunohistochemical patterns may explain some of the improvement in overall skin appearance after IMI therapy and may be related to the spectrum of signaling pathways induced by the imidazoquinolines.