AUTHOR INFORMATION	Section 1 of 10
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Author: Talib Najjar, DMD, MDS, PhD, Professor, Department of Oral and Maxillofacial Surgery, University of Medicine and Dentistry of New Jersey Coauthor(s): Thomas A Chiodo, DDS, Staff Dentist, Department of Oral and Maxillofacial Surgery, University of Medicine and Dentistry of New Jersey

Editor(s): Neil Shear, MD, Professor and Chief of Dermatology, Professor of Medicine, Pediatrics and Pharmacology, University of Toronto Medical School; Head of Dermatology, Sunnybrook Women's College Health Sciences Center, Canada; Michael J Wells, MD, Associate Professor, Department of Dermatology, Texas Tech University Health Sciences Center; M Joyce Rico, MD, Consulting Staff, Department of Dermatology, Fujisawa Healthcare, Inc; Glen H Crawford, MD, Assistant Clinical Professor, Department of Dermatology, University of Pennsylvania School of Medicine; Chief, Division of Dermatology, The Pennsylvania Hospital; and Dirk M Elston, MD, Director, Department of Dermatology, Geisinger Medical Center

Disclosure

	INTRODUCTION	Section 2 of 10
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Background: Melanoacanthoma is a rare condition of the cutaneous and mucosal epithelia that has been reported only in the last century. The lesion is characterized by a proliferation of both melanocytes and keratinocytes that results in pigmented macular or plaquelike lesions (see Image 1).

Initially, the cutaneous lesions were suspected to be malignant, and subsequently, the lesions were linked to a transformation to low-grade malignancy. Malignant transformation is reported in at least 2 cases; however, most lesions are generally considered benign and should be treated conservatively. No cases of recurrence or metastasis are reported in either the mucosal or cutaneous variants, although when examined clinically, the 2 types seem to have substantial differences. Cutaneous and mucosal melanoacanthoma differ in terms of patient age, patient race, and site.

In 1927, Bloch provided the earliest known description of melanoacanthoma, which was reported in the German literature (Schneider, 1981). Bloch described several skin lesions, which he originally called benign nonovoid melanoepithelioma of the skin. He further subdivided his cases into 2 types: In the histologic samples studied, type 1 had both dendritic melanocytes and keratinocytes, whereas the histologic appearance of type 2 was similar to that of type 1, but it lacked the dendritic melanocytes. Other authors have since redefined this type.

In 1960, Mishima and Pinkus reexamined the condition and further refined the diagnostic terminology (Wright, 1983). The condition that Bloch designated as type 1 is currently called melanoacanthoma, and type 2 is currently called pigmented seborrheic keratosis.

Although cutaneous lesions of melanoacanthoma were reported as early as 1927, Tomich et al at the American Academy of Oral Pathology first reported oral mucosal lesions in 1978 (Schneider, 1981). Although many authors subsequently published case reports, Goode et al published the first case report in 1983 (Goode, 1983). This was a retrospective review of 10 cases of oral melanoacanthoma reported in the literature.

To date, oral melanoacanthoma remains a rare condition, with approximately 25 reported cases. The cutaneous variant is also rare; however, it is more prevalent than the mucosal variant.

Pathophysiology: The cutaneous and mucosal variants of melanoacanthoma have similar histologic appearances. The lesion consists of proliferating melanocytes and keratinocytes, which result in large pigment-containing dendritic cells. The dendritic cells are present throughout the middle and upper layers of the epithelium.

The presence of inflammation in the mucosal variant is the factor that histologically differentiates the cutaneous and mucosal forms. Inflammation in the skin lesions is believed to be a secondary reactive phenomenon, and it is not related to the neoplastic process. Inflammation occurs almost universally in patients with mucosal lesions. The presence of inflammation and the spontaneous resolution of oral lesions are suggestive of a reactive process rather than a neoplastic process. The observation of trauma and inflammation associated with oral lesions has led to the conclusion that the mucosal variant is likely the result of a reactive process rather than a neoplastic process (Horlick, 1988).

Frequency:

• In the US: Oral melanoacanthoma is rare, with only approximately 25 cases observed since 1978, when the lesions were first reported. The cutaneous variant is more common, but it is still relatively rare among skin lesions. Among all the cases reported, specific patterns are described with respect to the race, sex, and age of patients with cutaneous melanoacanthomas and those with mucosal melanoacanthomas.

Race:

• Cutaneous lesions of melanoacanthoma are reported almost exclusively in white patients.

• The mucosal variant is reported almost exclusively in black patients.

• Some sporadic mucosal cases are reported in Asian individuals.

Sex: The prevalence for both variants of melanoacanthoma is fairly equal in both sexes, with a slight female predominance. The female-to-male ratio is approximately 3:2.

Age: The age distributions of the 2 types of melanoacanthoma differ (Chandler, 1997).

• Cutaneous lesions are found in patients with a mean age of approximately 60 years.

• Mucosal lesions appear in patients with a mean age of approximately 25 years.

	CLINICAL	Section 3 of 10
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History: Because the lesions of oral melanoacanthoma are not painful, physicians usually discover them on routine oral examination.

Physical: The clinical features of cutaneous and mucosal lesions may mimic those of other pigmented lesions. For example, the clinical and histologic features of oral melanoacanthoma lesions can resemble those of melanoma in situ.

• Cutaneous lesions

• Cutaneous lesions are reported in the scalp, eyelid, ear, nose, neck, thorax, and abdomen.

• Cutaneous lesions may be found on any area of the head and neck, as well as on the chest, abdomen, back, or legs.

• The lesions are generally asymptomatic, flat or slightly raised hyperpigmented areas.

• The color of the lesions ranges from brown to black to blue.

• Lesions are usually isolated, with no apparent precipitating factors.

• Lesions are slow growing and are usually present for months before treatment is sought.

• Mucosal lesions

• Mucosal lesions can occur in the buccal mucosa, labial mucosa, palate, gingiva (see Image 2), alveolar ridge, or lip.

• Although the appearance of mucosal lesions is similar to that of cutaneous lesions, mucosal lesions have a more rapid onset and rate of growth.

• Mucosal lesions occur mostly on the lip, buccal mucosa, or palate, and they are precipitated by a traumatic event.

• The diameter of the mucosal lesions can range from a few millimeters to several centimeters.

Causes: The role of trauma in the development of the lesion remains controversial, but any irritant must be removed.

	DIFFERENTIALS	Section 4 of 10
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Seborrheic Keratosis

Other Problems to be Considered:

Melanoma in situ
Melanosis
Superficial melanoma
Junctional melanocytic nevus
Melanotic macule
Pigmented basal cell epithelioma