Background
Strictly defined, osteoma cutis refers to the presence of bone within the skin in the absence of a preexisting or associated lesion. This is opposed to secondary types of cutaneous ossification that can occur in reaction to inflammatory, traumatic, and neoplastic processes.[1, 2]
Pathophysiology
Bone arises in skin and soft tissues through mesenchymal (membranous) ossification without cartilage precursors or models (as in endochondral ossification of the skeletal system).
The lesions of osteoma cutis differ from calcinosis cutis in that they represent bone formation (dermal deposition of hydroxyapatite crystals) versus calcium salt deposits.
The pathogenesis of primary osteoma cutis has the following two proposed mechanisms[3] :
Through mesenchymal cells differentiating into osteoblasts and then migrating to an abnormal location
Through an osteoblastic metaplasia of mesenchymal cells already in the dermis, such as fibroblasts
Etiology
Osteoma cutis can be a feature of several groups of patients. In can be secondary to inflammatory skin diseases, trauma/scars, and cutaneous tumors. It can also occur with genetic syndromes or in isolation.
Albright hereditary osteodystrophy is due to an autosomal dominant defect in the alpha subunit of intracellular G proteins.[4] The characteristic phenotype includes short stature, round facies, defective teeth, mental retardation, brachydactyly (fourth and fifth metacarpals/"knuckle knuckle dimple dimple" of the Archibald sign), and osteomas of the soft tissue and the skin. Classically, it presents with pseudohypoparathyroidism (elevated parathyroid hormone [PTH], hypocalcemia, hyperphosphatemia secondary to renal PTH resistance). Tetany is often the presenting sign, secondary to the low calcium level. Albright hereditary osteodystrophy can cause osteoma cutis without endocrine abnormalities in the pseudo-pseudohypoparathyroidism variant.
Progressive osseous heteroplasia is also, like Albright hereditary osteodystrophy, associated with a defect in the alpha subunit of G proteins (GNAS1 gene). It is characterized by ossification of the dermis in infancy, with progression to the subcutaneous and deeper connective tissues throughout childhood. It is not associated with endocrine changes, but it can have a severe affect on growth and joint mobility.[5]
Congenital platelike osteomatosis, a type of primary osteoma cutis, meets the following criteria:
Lesion present at birth (or within first year of life)
No evidence of abnormal calcium or phosphorous metabolism
No evidence of trauma or infection
Presence of at least one bony plate
Congenital platelike osteomatosis is most commonly found on the scalp. It should be monitored, as its diagnosis could be representative of a slow-evolving progressive osseous heteroplasia (something with much more severe consequences).[6]
Fibrodysplasia ossificans heteroplasia and fibrodysplasia ossificans progressiva (stone man syndrome) are possible causes.
Osteoma cutis can be found in patients with Gardner syndrome, which includes colonic polyposis, retinal hyperplasia, and other osseous and soft tissue growths.
Multiple miliary osteomas of the face often present in patients with a history of severe acne, sunburn, neurotic excoriation, or dermabrasion. These small, hard papules can have a bluish hue, especially in patients who have been exposed to tetracycline treatment.[7, 8]
Epidemiology
US frequency
Although considered rare, with no well-defined data on incidence, a plethora of conditions and syndromes may be found in association with osteoma cutis. Hence, the frequency of its occurrence varies accordingly. Primary lesions with no underlying cause are even rarer, but they account for approximately 20% of all skin ossifications. Reported in 1977, of 20,000 consecutive skin biopsies, only 35 cutaneous osteomas were found. Ten of them were primary, while 25 appeared secondary to another abnormality (although long ago, this allows some insight into its rarity).[1, 2]
Race
No particular race is predisposed to developing osteoma cutis.
Sex
Generally, no distinct sexual predominance exists. However, one cause of osteoma cutis, Albright hereditary osteodystrophy, occurs with a female-to-male ratio of 2:1.
Age
Osteoma cutis may occur at any age. Of note, multiple miliary osteoma cutis classically presents in middle-aged white women.[7]
Prognosis
Osteoma cutis is not life threatening, although local discomfort and/or disfigurement may lead the patient to seek consultation. Osteosarcoma or other malignancies have not been reported to arise within osteoma cutis.
History
Patients may report having hard areas in the skin. A familial occurrence of Albright hereditary osteodystrophy may be present.
Physical Examination
The presentations of osteoma cutis can be highly variable, with clinical entities that are defined by the number, the form, and the location of the lesions. There are four clinical types: isolated, widespread, multiple miliary facial, and platelike osteomas. Hence, they may present as single or multiple hard nodules, miliary tumors, or plaques.[9, 5] The face, scalp, extremities, digits, and subungual areas are most commonly affected.
See the images below.
View Image | Solitary nodule on the frontal part of the scalp. |
View Image | Miliary cutaneous osteomata. Multiple, small, bluish, stony-hard nodules in an acneiform distribution along the cheeks. |
Approach Considerations
Rare and unusual situations can arise at times. Histologic evaluation has identified extramedullary acute leukemia (myeloid sarcoma) arising in an isolated preexisting osteoma cutis.[10] Biopsy and histologic evaluation are warranted in any unusual lesion or clinical situation.
Laboratory Studies
Serum calcium, phosphorous, and parathyroid hormone (PTH) levels help to define Albright hereditary osteodystrophy.
Imaging Studies
Plain radiographs demonstrate lesions but are not necessary for diagnosis.
Procedures
Excisional biopsy can be performed for diagnosis, relief of discomfort, and cosmesis.
Histologic Findings
Small spicules to large masses of mature bone are found in the dermis or extend into the subcutaneous tissue. Spicules of bone may enclose areas of mature fat, recapitulating a medullary cavity, but hematopoietic elements are seldom observed.
See the images below.
View Image | A microscopic view of osteoma cutis shows well-formed mature trabecular bone just beneath the epidermis. Note the absence of hematopoietic elements in.... |
View Image | Osteoma cutis is often identified as an incidental finding on examination of re-excision specimens. This excisional specimen failed to reveal residual.... |
View Image | High-power examination reveals adipocytes centrally and a prominent calcified matrix surrounded by osteoid. |
Medical Care
Removal by excision or laser resurfacing to unroof overlying skin may be performed.[11] Treatment with the Er:YAG laser may result in less hypopigmentation and scarring than with the carbon dioxide laser.[12]
Other reported treatments with unproven efficacy include the following:
Consultations
When several lesions are noted, especially in pediatric patients, evaluation for associated syndromes may be warranted.
Author
Luke Lennox, MD, Resident Physician, Department of Dermatology, Case Western Metro Health Medical Center
Disclosure: Nothing to disclose.
Coauthor(s)
Thomas N Helm, MD, Clinical Professor of Dermatology and Pathology, University of Buffalo, State University of New York School of Medicine and Biomedical Sciences; Director, Buffalo Medical Group Dermatopathology Laboratory
Disclosure: Nothing to disclose.
Specialty Editors
David F Butler, MD, Former Section Chief of Dermatology, Central Texas Veterans Healthcare System; Professor of Dermatology, Texas A&M University College of Medicine; Founding Chair, Department of Dermatology, Scott and White Clinic
Disclosure: Nothing to disclose.
Rosalie Elenitsas, MD, Herman Beerman Professor of Dermatology, University of Pennsylvania School of Medicine; Director, Penn Cutaneous Pathology Services, Department of Dermatology, University of Pennsylvania Health System
Disclosure: Received royalty from Lippincott Williams Wilkins for textbook editor.
Chief Editor
William D James, MD, Paul R Gross Professor of Dermatology, Vice-Chairman, Residency Program Director, Department of Dermatology, University of Pennsylvania School of Medicine
Disclosure: Received income in an amount equal to or greater than $250 from: Elsevier; WebMD.
Additional Contributors
James W Patterson, MD, Professor of Pathology and Dermatology, Director of Dermatopathology, University of Virginia Medical Center
Disclosure: Nothing to disclose.
Acknowledgements
Kevaghn P Fair, DO Consultant Pathologist and Founder, Dominion Pathology Laboratories
Kevaghn P Fair, DO is a member of the following medical societies: American Society for Clinical Pathology, American Society of Dermatopathology, and College of American Pathologists
Disclosure: Nothing to disclose.
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