Background
Melanoacanthoma is a term that Mishima and Pinkus [1] introduced in 1960 to describe a pigmented, benign proliferation of both keratinocytes and dendritic melanocytes. Prior to this designation, Bloch [2] described a similar lesion in 1927 that he called melanoepithelioma type I. Melanoepithelioma type II is an ordinary pigmented seborrheic keratosis.
Oral melanoacanthoma is a rare, reactive, mucosal lesion, which, similar to cutaneous melanoacanthoma, is associated with hyperplasia of spinous keratinocytes and melanocytes. [3] Its most common intraoral sites are the buccal mucosa, lip, palate, and gingiva. [4, 5, 6, 7] Melanocytes occur throughout the oral mucosa, but they have a relatively low level of pigment production and may go unrecognized. [8] The average age at presentation is 28 years, and it occurs mainly in blacks, with a strong female predilection. [9] Oral melanoacanthoma is unrelated to seborrheic keratosis. Oral melanoacanthoma is most often seen as an enlarging flat or slightly raised area of hyperpigmentation on the buccal mucosa of adult black women. Strong homatropine methylbromide reactivity has been described, limiting its utility in distinguishing oral melanoacanthoma from malignant melanoma. Laugier-Hunziker syndrome, also known as idiopathic lenticular mucocutaneous hyperpigmentation, displays progressive mucosal pigmentation. It has been described with multiple metachronous oral melanoacanthomas. [10]
Pathophysiology
Although melanoacanthoma can be found both on the skin and oral mucosa, the focus of this review is cutaneous melanoacanthoma. Although most authors consider cutaneous melanoacanthoma a benign tumor of melanocytes and keratinocytes, some have suggested it may be a reactive phenomenon induced by localized trauma. [11]
Etiology
The cause of melanoacanthoma is unknown, but most instances appear to represent a benign neoplasm. Irritation or trauma to the skin may cause some cutaneous melanoacanthomas, especially on the lips. Trauma and irritation of the oral mucosa are believed to cause oral melanoacanthoma.
Epidemiology
Frequency
United States
Cutaneous melanoacanthoma is generally regarded as rare. Melanoacanthoma was the primary diagnosis in 5 of 500,000 consecutive skin biopsy samples in one series from the United States. [12]
International
In their series of 189 consecutive seborrheic keratoses diagnosed among Spanish patients, Simon et al [13] found that cutaneous melanoacanthoma represented 28% of all seborrheic keratoses. A Korean survey of seborrheic keratoses classified 9.2% of 271 as melanoacanthomas. [14]
Race
Cutaneous melanoacanthoma is described more frequently white patients than in others. However, the lesion is rare in all ethnic groups.
Sex
Cutaneous melanoacanthoma develops in males and females with the same frequency.
Age
Cutaneous melanoacanthoma develops in middle-aged and elderly people. Melanoacanthoma has been described in patients aged 46-81 years, with an average age of 55-65 years. [12, 15]
Prognosis
Melanoacanthoma is benign. Removal of cutaneous melanoacanthoma is curative.
Morbidity with melanoacanthoma is uncommon. However, a melanoacanthoma that extends from the upper eyelid to beyond the lower eyelid can obstruct the patient's vision. The authors have observed this complication. Melanoacanthomas may be as large as 10 cm in diameter and can therefore be unappealing to the patient. [16]
Patient Education
Patients should be informed that cutaneous melanoacanthoma is benign and has no potential for malignant transformation. Cutaneous melanoacanthoma is not associated with any skin or visceral cancer; it is not an indicator of cancer, and its presence is not a risk factor for cancer.
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Large cutaneous melanoacanthoma in a 45-year-old man that obstructs his vision.
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Photomicrograph of cutaneous melanoacanthoma. Large polydendritic melanocytes are seen at all levels of the epidermis. Acanthosis, hyperkeratosis, and slight papillomatosis are also present (hematoxylin and eosin stain, original magnification X139).
