Perforating Osteoma Cutis of the Foot: A Case Study of a Misidentified Verrucca Plantaris

Perforating osteoma cutis is a rare subtype of osteoma cutis characterized by ectopic osseous deposits within the epidermal layers of skin. Through a process called transepidermal elimination, these osseous deposits are expressed through these layers, often creating ulcerations. Osteoma cutis is a benign process best understood as an inflammatory response that induces mesenchymal differentiation of fibroblasts into an osseous byproduct; however, no specific pathophysiology has been identified. To the authors' knowledge, perforating osteoma cutis has been reported only seven times in the literature, with no reports involving the foot and ankle. In this case study, we present a 21-year-old female with no significant past medical history who presented with a recurrent lesion to her plantar first metatarsophalangeal joint (MPJ). The patient had previously been misdiagnosed with a verruca plantaris. An excisional biopsy was performed, serving both diagnostic and therapeutic purposes. Clinical and histopathologic analysis were consistent with perforating osteoma cutis. While previous papers have noted occasional cases of osteoma cutis on the foot, the authors feel the specific subtype of perforating osteoma cutis often appears with an ulcerated lesion, which is important to differentiate for appropriate treatment.