The Ring Verruca Plantaris in Cantharidin Use

Verrucae (warts) are the most common viral infections of the skin, affecting 7% to 10% of the general population. Typically caused by human papillomavirus type 1, plantar warts manifest as benign proliferation of the epithelial cells on the feet. It has been cited that up to one-third of nongenital warts become recalcitrant, and biopsy is often required to confirm diagnosis and direct appropriate treatment. These treatments can vary from various types of oral medications, acids, ablative modalities, and injections. In this article, we present a case of a recalcitrant plantar wart that appeared to circumferentially spread from the initial site after first-line treatment and presumed resolution with the product cantharidin. The development of ring warts is a known complication associated with cantharidin use, with little described rationale to the presentation.