Painful toe ulcers

Diagnosis: Osteoma cutis

Lesional biopsies revealed that the patient had osteoma cutis, a skin condition in which bone ossification (including lamellae, trabecular bone formation, osteocytes, and sometimes marrow) occurs within the dermis.

A rare condition
Osteoma cutis has an incidence of 1.2-1.7 cases per 1000 skin lesion biopsies.¹ The primary form of osteoma cutis occurs in about 25% of cases and is associated with certain genetic disorders such as Gardner’s syndrome and Albright’s hereditary osteodystrophy; it arises without a preexisting lesion.¹ The secondary type of osteoma cutis—which our patient had—often arises within a cancerous lesion (especially melanocytic nevi and basal cell carcinoma) or chronic inflammation (as is found in traumatic scars, acne vulgaris, chronic venous stasis, vasculitis, and other nonspecific inflammatory conditions).^1-3

Sixty-eight percent of osteoma cutis cases are benign, and most patients are white females.¹ Most lesions arise on the head, neck, and digits.^1,4 Although foot lesions are much less common, a few cases of secondary osteoma cutis on the foot have been reported.^4,5

Osteoma cutis is believed to arise via mesenchymal ossification (in contrast to endochondral bone formation from a cartilaginous precursor). Proposed mechanisms include aberrant embryological migration of mesenchymal cells into the dermis and metaplastic transformation of fibroblasts into osteoid-producing osteoblasts.⁴

Is it osteoma cutis or calcinosis cutis?

The differential includes calcinosis cutis, or deposition of insoluble calcium compounds in the skin without true bone formation. Lesions of both osteoma cutis and calcinosis cutis are sometimes palpable and seen on x-ray,² but more often, plain radiographs are normal.³

Making the diagnosis requires a high suspicion for the condition—especially in patients without peripheral vascular disease or neuropathy who have nonhealing or slow-healing ulcers. A good patient history is also important to help rule out possible uncommon causes, such as cutaneous tuberculosis.⁶