Highlights
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Perforating osteoma cutis is characterized by transepidermal elimination.
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Perforating osteoma cutis often presents as an ulcerated lesion.
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Routine treatment includes a 3:1 elliptical excision of the lesion.
Abstract
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.
Introduction
Perforating osteoma cutis is an extremely rare subtype of osteoma cutis characterized by a central crater of osseous material enclosed by squamous epithelium, often corresponding to a transepidermal channel, from which it is eliminated. In such rare cases, the overlying epidermis may become ulcerated with the release of bony spicules, known as transepidermal elimination. Osteoma cutis can be subdivided into two overarching subtypes: primary and secondary. Primary osteoma cutis occurs de novo with no history of prior disease, while secondary osteoma cutis develops in association with prior trauma, neoplasm, or inflammatory disease. An overwhelming majority of reported cases are secondary, accounting for 85%, while primary cases account for only 15%. These lesions are most often noted in females with a peak incidence in the second and third decades; cases in both children and men have also been reported. Lesions are most commonly located on the face in females and on the scalp in men, although they can also occur on the chest and, less frequently, the extremities. , The subtype of perforating osteoma cutis is extremely rare, with only seven previously documented cases and no reported cases to the foot and ankle, to the authors’ knowledge.
Case report
Our patient is a 25-year-old female who presented to the clinic with a chief complaint of a benign-appearing lesion on the plantar aspect of the first metatarsophalangeal joint (MPJ) measuring approximately 0.5 cm in diameter. Past medical history was significant for migraines. The patient denied additional medical conditions, medications, allergies, prior surgeries, and tobacco use. Physical exam was otherwise unremarkable aside from the previously described lesion.
The patient was initially evaluated at an outside office and diagnosed with a verruca plantaris (plantar wart). After failed treatment, she was re-evaluated by an additional podiatrist and dermatologist, both diagnosing the lesion as a plantar wart. The patient continued to experience persistence of the lesion and attempted self-treatment using over-the-counter keratolytics and bandaging the area. Following self-treatment, she noted significant edema and black discoloration of the lesion, causing her to present to an urgent care. At the urgent care, an abscess was identified, and incision and drainage were performed. Cultures obtained from the purulent drainage identified an MRSA infection. She was subsequently started on trimethoprim-sulfamethoxazole (Bactrim). The patient was referred to our clinic for a second opinion.
On examination, the lesion demonstrated no capillary budding or loss of skin lines, suggesting that the lesion was not verrucous in nature. The previous infection had resolved. Given the length of failed conservative treatment and the appearance inconsistent with a verruca, a decision was made to perform an excisional biopsy of the skin lesion in the operating room.
The patient was brought to the operating room and underwent monitored anesthesia care with local anesthetic infiltration. The patient’s foot was prepared and draped in standard sterile fashion. The operative site was infiltrated with local anesthetic. Surgical excision was performed using a 3:1 elliptical excision. Using a sharp 15-blade, an incision was carried through the dermis into the subcutaneous tissue. The lesion was removed and sent for histopathologic evaluation. The incision was closed with non-absorbable sutures, and the patient was placed in a post-operative shoe and allowed to weight-bear as tolerated.
All material was sent for histopathologic evaluation. The tissue was sectioned and stained with hematoxylin and eosin (H&E). The report demonstrated “multiple sections… [with] the presence of dense eosinophilic deposits in the dermis with spicules of bone perforating the epidermis in the process of transepidermal elimination. There is a central zone of ulceration and epidermal necrosis with associated impetiginized serum crust, hemorrhage, and fibrin deposition.”. The final diagnosis of the pathologist was consistent with perforating osteoma cutis Figs. 1 and 2 .
