Imiquimod reactivation of lichen planus.

A 44-year-old man who was previously diagnosed with actinic cheilitis was prescribed imiquimod cream 5%, which resulted in thick hemorrhagic crusting of the lower lip after 4 applications. He subsequently noted the development of lichen planus lesions on his arms and legs for the first time in 15 years following imiquimod use. On follow-up he also was noted to have characteristic Wickham striae on his lower lip. Lichen planus is an autoimmune inflammatory condition in which autoreactive T lymphocytes attack keratinocytes. The mechanism of action for imiquimod is upregulation of IFN-alpha and IFN-beta. Treatment with clobetasol cream 0.05% led to resolution of his lichen planus lesions.