Oral Melanotic Macule
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Large brown macule of the soft palate has irregular borders.

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Introduction

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The oral mucosa is usually not pigmented despite the fact that it has the same density of melanocytes as the skin. Occasional patients, however, will show a focal area of melanin deposition, either as a response to local chronic conditions (mechanical trauma, tobacco smoking, chronic autoimmune mucositis), racial background (the darker a person's skin color the more likely they are to have oral pigmentation), or systemic medications, especially chloroquine. Moreover, certain syndromes and systemic diseases have oral pigmentation as part of their spectrum (Table 1), as mentioned previously in this section.

Most focal melanin deposits of the oral mucosa which are not associated with race or an appropriate syndrome are innocuous surface discolorations called oral melanotic macule (focal melanosis). This entity represents not only a focal increase in melanin deposition but a concomitant increase in the number of melanocytes. Unlike the cutaneous ephelis (freckle), the oral melanotic macule is not dependent on sun exposure, nor does it show the elongated rete ridges of actinic lentigo. Some authorities have questioned the purported lack of an association with actinic irradiation for melanotic macule located on the vermilion border, preferring to consider the lesion at this site to be a distinct entity called labial melanotic macule. Melanotic macules are found in the mouths of 1 of every 1,000 adults (Table 2).

Clinical Features

the oral melanotic macule has a 2:1 female predilection with an average age of 43 years at the time of diagnosis, although it can develop at any age. One-third of lesions occur on the vermilion border of the lower lip, but the buccal mucosa, gingiva and palate are other sites of common occurrence. Almost a fifth of the lesions are multiple.

The typical macule is a well-demarcated, uniformly tan to dark brown, asymptomatic, round or oval discoloration less than 7 mm. in diameter (Figure 1). The lesion is not thickened and has the same consistency as surrounding mucosa. It tends to have an abrupt onset and seldom enlarges after diagnosis.

A special case of oral melanosis, called smoker's melanosis (Figure 2), is found on the gingival or buccal mucosa in heavy smokers. It has an adult onset and is often associated with a concomitant superficial white/gray keratosis. The keratosis may become thick enough to mimic leukoplakia, although it is not known whether or not it is a true precancer. Both the pigmentation and the keratosis diminish or disappear once the tobacco habit is stopped.

While the melanotic macule is an innocuous lesion, it must be remembered that focal oral and oropharyngeal pigmentation might represent an internal malignancy (usually lung), an oral manifestation of a systemic disease or one facet of a genetic syndrome (Table 1).

Pathology and Differential Diagnosis

The oral melanotic macule is characterized by an otherwise normal stratified squamous epithelium with abundant melanin deposits within the keratinocytes of the basal and parabasal layers (Figures 3 & 4). Deposits may also be seen within subepithelial stroma (melanin incontinence), perhaps within macrophages or melanophages (Figure 5). There is no underlying inflammatory response. The melanin can be distinguished from iron deposits with melanin stains or by the loss of brown color after bleaching. Brown formalin deposits can be differentiated by their association with erythrocytes rather than with basal layer epithelial cells.

Treatment and Prognosis

No treatment is required for oral melanotic macule except for esthetic considerations. The intraoral melanotic macule has no malignant transformation potential, but an early melanoma could have a similar clinical appearance. For this reason, pigmented macular lesions of recent onset, large size, irregular pigmentation, unknown duration, or with a history of recent enlargement should be excised and examined histopathologically.

References (Chronologic Order)

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Specific references:

Barrett AW, et al. Oral melanotic macules that develop after radiation therapy. Oral Surg Oral Med Oral Pathol 1994; 77:431-434.

Pictures

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