Treatment of Lentigomaligna in Dark Skin with Topical Imiquimod Results in Dark Hyperpigmentation

LentigoMaligna (LM) is an in situ lesion with a low risk of progression to LM Melanoma (LMM). Treatment of LM is mostly advocated because an invasive component of LMM might be lethal. Recently topical Imiquimod 5% cream was introduced as a new treatment possibility. We describe here a patient, with skin type IV, with a hyperpigmented LM eruption at his forehead. The lesion was treated 4 weeks with topical Imiquimod 5%, 5 times a week for 8 weeks. Four weeks after cessation of treatment the macular lesion appeared enlarged and darker indicating lack of response. Punch biopsies revealed post-inflammatory hyperpigmentation (PIH) and ruled out LM and LMM. During 6 moths observation the skin normalized. The present case is a reminder that dark skin comprises an increased risk of PIH that when induced by Imiquimod treatment of LM can be mistaken as lack of therapeutic efficacy or progression to LMM.