A Rare Case of Miliary Osteoma Cutis of the Lower Extremity Causing Chronic Transepidermal Eruption over a 10-Year Period

Summary: Miliary osteoma cutis (MOS) is a rare cutaneous entity that classically arises as an uncommon, late-term sequelae of acne vulgaris. Histologically, it is characterized by multifocal, ectopic formation of lamellar bone in dermis. Herein, we present an unusual case of a 69-year-old female who presented with multiple pruritic nodules localized on her left anterior shin. The patient reported these lesions first appeared when she was 19 years of age. Physical examination revealed firm papules with superficial erosions and central nodules overlying a patch of hyperpigmentation. Review of systems was negative for prior trauma to the extremities and for renal dysfunction. Routine laboratory and infectious testing was negative. In the ensuing ten year period, several biopsies displayed persistent miliary osteoma cutis with transepidermal elimination. Application of topical hydroquinone, tretinoin, urea, and ammonium lactate were trialed as treatment, though the patient has continued to develop new lesions at the same site. Consequently, we present a rare case of persistent miliary osteoma cutis of the lower extremity with chronic transepidermal eruption over a ten-year period.