Effect of imiquimod on partial-thickness burns

Burns can result in substantial morbidity through fibroblast proliferation and contracture. Imiquimod (IMQ), an immune response modifier and upregulator of endogenous cytokine expression, has been shown to suppress fibroblast proliferation. It is widely used in the treatment of viral, neoplastic and non-neoplastic skin conditions and has recently been tested in the reduction of hypertrophic scarring and keloids. To our knowledge, no other study has so far evaluated the effect of IMQ on cutaneous burns.

Partial-thickness burns were produced on the dorsum of 32 Wistar rats. Right-sided wounds received saline and left-sided wounds received 5% IMQ cream three times/week following injury. Photographs taken on post-burn days (PBD) 4, 7, 14 and 21 were evaluated for wound appearance using a clinical assessment scale and a visual analog scale. Scars were measured by digital planimetry. Samples stained with hematoxylin-eosin were submitted to conventional histological analysis. Samples stained with Sirius Red were analyzed under polarized light for collagen morphometry.

Visual scores were higher in the saline group on PBD 21 (p<0.05). Wound edge migration rates were lower (p<0.05) and conventional histology showed accentuated inflammation and delayed reepithelialization in the IMQ group. Type-I and type-III collagen deposition increased in the saline group and decreased in the IMQ group. Conversely, the proportion between type-I and type-III collagen differed significantly between treatments on PBD 4 and 21 (p<0.05 in both cases).

Short-term topical imiquimod treatment of partial-thickness burns in rats did not improve clinical appearance and scarring but rather decreased fibrosis. Significant differences in collagen deposition were observed between the treatments.