CONTRERAS E, CARLOS R. ORAL MELANOACANTHOSIS (MELANOACHANTOMA): REPORT OF A CASE AND REVIEW OF THE LITERATURE. MED ORAL PATOL ORAL CIR BUCAL 2005;10:9-12.

ABSTRACT

Oral melanoacanthosis (MA) is a rare pigmented mucosal lesion that is considered the counterpart of cutaneous melanoacanthoma. Microscopically the superficial epithelium shows mild to moderate acanthosis, spongiosis and prominent dendritic melanin producing melanocytes, which are present throughout the spinous keratinocytes. Reported cases show predilection for black females and the most common locations in decreasing frequency are buccal mucosa, lip, palate and gingiva. Although its pathogenesis remains uncertain, its clinical behavior is sugestive of a reactive origin. The clinical appearance of oral MA is non diagnostic and therefore biopsy is mandatory to differentiate from other melanocytic lesions, including melanoma.

Key words: Melanoacanthoma, pigmented, oral

INTRODUCTION

In 1960 Mishima and Pinkus introduced the term melanoacanthoma, as an attempt to clarify the terminology of melanoepithelioma types 1 and 2 previously described by Bloch in 1927 (1). The term melanoacanthoma corresponded to Bloch´s type 1 melanoepithelioma. The first lesion reported in the oral mucosa was presented by Tomich and Dorey at the Annual Meeting of the American Academy of Oral and Maxillofacial Pathology in 1978. The first published case, to the best of our knowledge was reported by Schneider et al in 1981 (2).

Solitary and occasional multiple lesions affecting the oral mucosa had been reported in the literature, with a total of 38 cases to date. The published data show a striking predilection for black females with an age range of 5 to 77 years, with most cases present in the 3th and 4th decades. The buccal mucosa is the most commonly affected site, but the lips, gingiva and palate are also involved, suggesting that masticatory and frictional trauma may play an etiologic role (3).

MA is therefore considered a reactive lesion and its reversible nature has been previously documented, but such event is considered rare (3, 4). Based on this fact, we agree with the term melanoacanthosis first introduced by Tomich and Zunt in 1990 (5).

Microscopically MA is characterized by the presence of numerous benign appearing dendritic melanocytes scattered through an acanthotic and mature squamous cell epithelium. Basal layer melanocytes may be increased in number and spongiosis is a common finding. In addition inflammatory cells with eosinophils may be present in the subjacent connective tissue stroma (6.)

Fornatora et al. (7) in a recent publication reported strong reactivity of MA to HMB45, demonstrating the limited utility of this antibody in distinguishing MA from melanoma.

Biopsy is mandatory to rule out melanoma and once the diagnosis is established, no further treatment is usually required.

CASE REPORT

On June 2003, a 40 year old Guatemalan female was referred to our service due to an asymptomatic pigmented dark-brown macule that was discovered during routine dental examination. The lesion was located on the hard palate and measured 0.5 cm in greatest diameter (Fig. 1). The patient weared a partial removable prosthesis that caused erythema of the underlying mucosa. Fungal organisms were negative on cytologic smear. An excisional biopsy was performed under local anesthesia, using a 0.6 cm punch.

The biopsy revealed the presence of dendritic melanocytes in the spinous layer of the surface epithelium, which was mildly acanthotic and spongiotic (Fig. 2, 3). Beneath the surface epithelium a mild chronic inflammatory infiltrate was present in the lamina propria along with melanin pigment and melanophages. The lesion was signed out as MA. The biopsy site healed completely without complications.

DISCUSSION

The differential diagnosis of a solitary deeply brown-black pigmented lesion includes nevi, oral melanotic macule, submucosal hemorrhage, melanoacanthosis, amalgam tattoo and melanoma.

Intraoral nevi are distinctly uncommon. Most arise on palate or gingiva. Melanocytic nevi are classified histopathologically according to their stage of development, which is evidenced by the relationship of the nevus cells to the surface epithelium and underlying connective tissue. Most intraoral melanocytic nevi are classified microscopically as intramucosal nevi (6).

The vermilion zone of the lower lip is the most common site of occurrence of the oral melanotic macule, followed by the buccal mucosa, gingiva and palate. Microscopically is characterized by increase in the amount of melanin, and perhaps melanocytes in the basal and parabasal layer of normal stratified squamous epithelium (8).

Lesions of vascular origin might also be considered. These include submucosal hemorrhage, hematoma, varix, and hemangioma. Diascopy (compression) ruled out the last two lesions.

Amalgam tattoo, or focal argyrosis, is an iatrogenic lesion that follows traumatic soft tissue implantation of amalgam particles. They may be detected on soft tissue radiographs. Microscopically, amalgam particles are typically aligned along collagen fibers and blood vessels, few lymphocytes and macrophages are also found (9).

The upper gingiva and hard palate are common sites for oral melanoma. Primary melanoma of the oral cavity is a rare malignancy, accounting for 0.2% to 8% of all melanomas in Europe and United States. Black Africans, Asians, Native Americans and Hispanics are more commonly affected (10). Therefore the important value of the biopsy in this case to rule out melanoma.

The diagnosis of melanoacanthosis in a mestizo Guatemalan female reflects that this lesion can affect racial or ethnic groups other than blacks.

In the present case is important to note the proximity of the lesion to a prosthetic device which could be related in its pathogenesis, considering that trauma or frictional irritation has been mentioned as potential etiologic factors.

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